Adhesive for electroless plating, feedstock composition for preparing adhesive for electroless plating, and printed wiring board

ABSTRACT

The adhesive for electroless plating which is advantageous to ensure insulation reliabilities between lines and between layers while maintaining a practical peel strength, and the printed circuit board using the adhesive are disclosed. The adhesive is formed by dispersing cured heat-resistant resin particles soluble in acid or oxidizing agent into uncured heat-resistant resin matrix hardly soluble in acid or oxidizing agent through curing treatment, in which the heat-resistant resin particles have an average particle size of not more than 1.5 mum.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to an adhesive for electroless plating, materialcomposites for preparing the adhesive for electroless plating and aprinted circuit board, and more particularly to an adhesive forelectroless plating suitable for the formation of fine pattern capableof ensuring an insulation reliability between lines while maintaining apractical peel strength in a semi-additive process or guaranteeing aninsulation reliability between lines even at high temperature and highhumidity conditions while maintaining a practical peel strength in afull-additive process, material composition for preparing the adhesive,and a printed circuit board using the adhesive.

2. Discussion of Background Information

Recently, so-called build-up multilayer circuit board is noticed from ademand for high densification of multilayer circuit boards. Thisbuild-up multilayer circuit board produced by a method as described, forexample, in JP-B-4-55555. That is, an interlaminar resin insulatingagent composed of a photosensitive adhesive for electroless plating isapplied onto a core substrate, dried, exposed to a light and developedto form an interlaminar insulating resin layer having openings forviaholes, and then the surface of the interlaminar insulating resinlayer is roughened by treating with an oxidizing agent or the like, anda plating resist is formed on the roughened surface by subjecting aphotosensitive resin layer to light exposure and development treatments,and thereafter a non-forming portion of the plating resist is subjectedto an electroless plating to form a conductor circuit pattern inclusiveof viaholes, and next such steps are repeated plural times to obtain amultilayered build-up circuit board through an additive process.

In the build-up circuit board produced by such a method, the adhesivefor electroless plating obtained by dispersing soluble cured resinparticles consisting of rough particles having an average particle sizeof 2-10 μm and fine particles having an average particle size of notmore than 2 m into a heat-resistant resin matrix hardly soluble througha curing treatment as disclosed in JP-A-63-158156 and JP-A-2-188992(U.S. Pat. Nos. 5,500,321, and 5,519,177) is used in the interlaminarinsulating resin layer.

Furthermore, JP-A-61-276875 (U.S. Pat. Nos. 4,752,499, and 5,021,472)discloses an adhesive for electroless plating obtained by dispersingsoluble cured epoxy resin powder ground into an average particle size of1.6 μm in a hardly soluble heat-resistant resin matrix.

The interlaminar insulating resin layer formed on the substrate usingthe above adhesive is roughened on its surface by dissolving andremoving the heat-resistant resin particles existing in the surface areaand is excellent in the adhesion property to a conductor circuit formedon the roughened surface through the plating resist.

However, the build-up circuit board retaining the plating resist as apermanent resist such as the circuit board produced by the full-additiveprocess is bad in the adhesion property at the boundary between thepermanent resist and the conductor circuit. Therefore, this build-upcircuit board has a problem that when IC chip is mounted on the board,cracks are generated in the interlaminar insulating resin layer startingfrom a boundary between the plating resist and the conductor circuitresulted from a difference of thermal expansion coefficient.

On the contrary, a method of removing a plating resist and subjecting atleast a side face of a conductor circuit to a roughening treatment toimprove the adhesion property to an interlaminar insulating resin layerformed on the conductor circuit has hitherto been proposed as atechnique capable of obstructing cracks created on the interlaminarinsulating resin layer. As a method of producing a circuit boardadvantageously utilizing this method, mention may be made of thesemi-additive process.

In the semi-additive process, the surface of the interlaminar insulatingresin layer is first roughened and an electroless plated film is thinlyformed over a full roughened surface and then a plating resist is formedon a non-conductor portion of the electroless plated film and further anelectrolytic plated film is thickly formed on a no-resist formingportion and thereafter the plating resist and the electroless platedfilm located below the plating resist are removed to form a conductorcircuit pattern.

However, the build-up circuit board produced through the semi-additiveprocess using the above adhesive has a problem that the electrolessplated film remains in a depression (anchor) of the roughened surface ofthe adhesive layer located under the resist to lower the insulationreliability between the lines.

And also, the build-up circuit board produced through the full-additiveprocess using the above adhesive has a problem that the value ofinsulation resistance between the conductor circuits lowers under hightemperature and high humidity conditions.

Moreover, the circuit boards produced through the full-additive processand semi-additive process have a problem that the interlaminarinsulation is broken if the adhesive contains relatively largeheat-resistant resin particles having an average particle size of notless than 2 μm.

The invention proposes a technique for solving problems inherent to thecircuit board produced through the above full-additive process orsemi-additive process. The present invention provides an adhesive forelectroless plating which is advantageous to ensure insulationreliabilities between lines and between layers while maintaining apractical peel strength. The present invention also provides a printedcircuit board having an excellent reliability by using the aboveadhesive for electroless plating.

On the other hand, the above-mentioned adhesive for electroless plating,in case the printed circuit boards are industrially massproduced,require to be preserved from the beginning of manufacturing up to theactual process of coating on the substrate.

For this reason, the adhesive for the electroless plating has drawbacksthat a curing gradually proceeds or viscosity becomes high due togelation during the preservation.

The present invention further provides an adhesive for the electrolessplating which is capable of supressing the curing of the adhesive whichis generated inevitably in the course of preservation, and to provide amethod of manufacturing the printed circuit board using thus obtainedadhesive for the electroless plating.

SUMMARY OF THE INVENTION

The inventor has made various studies in order to achieve the presentinvention and considered that the occurrence of the above problemsresults from the fact that the average particle size of theheat-resistant resin particles to be dissolved and removed is too largeand found the following knowledge.

That is, the interlaminar insulating resin layer consisting of the aboveadhesive obtained by dispersing soluble resin particles comprised ofrough particles having an average particle size of 2-10 μm and fineparticles having an average particle size of not more than 2 μm is thata depth of a depression in a roughened surface formed on the surface ofthis layer is about 10 μm (e.g. Example 1 of JP-A-7-34048 (U.S. Pat. No.5,519,177)). Therefore, it is considered that since the electrolessplated film is formed in the depth portion of the depression through thesemi-additive process, it can not be removed completely and is retainedto degrade the insulating property between lines. On the other hand, inthe full-additive process, the surface area becomes large as thedepression in the roughened surface becomes deep, and a great number ofpalladium being a catalyst nucleus of the electroless plated filmbeneath the plating resist between lines. As a result, it is consideredthat the palladium reacts with chlorine ion or the like in theheat-resistant resin under conditions of high temperature and highhumidity to form a conductive compound to thereby lower the insulatingproperty between lines.

When the heat-resistant resin particles having an average particle sizeof not less than 2 μm are existent in the interlaminar insulating resinlayer, gaps are apt to be created by the roughening treatment, so thatit is considered that the plated film is precipitated into the gaps toelectrically connect the upper layer conductor circuit to the lowerlayer conductor circuit to thereby break the interlaminar insulation.

Based on the above knowledge, the inventor developed the adhesive forelectroless plating having the following features.

(1) The adhesive for electroless plating according to the presentinvention is an adhesive for electroless plating formed by dispersingcured heat-resistant resin particles soluble in acid or oxidizing agentinto uncured heat-resistant resin matrix hardly soluble in acid oroxidizing agent through curing treatment, characterized in that theheat-resistant resin particles have an average particle size of not morethan 1.5 μm, preferably 0.1-1.0 μm.

It is preferred that the heat-resistant resin particles are sphericalparticles and have a particle size distribution that a particle size ofa peak in the distribution is not more than 1.5 μm and the peak of thisdistribution is one.

Further, the printed circuit board according to the present invention ischaracterized by having the following construction.

(2) In a printed circuit board comprising a substrate, a cured adhesivelayer for electroless plating having a roughened surface, and aconductor circuit formed on the roughened surface of the adhesive layer,

said circuit is characterized by the adhesive layer for electrolessplating formed by dispersing cured heat-resistant resin particlessoluble in acid or oxidizing agent into uncured heat-resistant resinmatrix hardly soluble in acid or oxidizing agent through curingtreatment, and characterized by the heat-resistant resin particleshaving an average particle size of not more than 1.5 μm, preferably0.1-1.0 μm.

It is preferred that the heat-resistant particles are sphericalparticles and have a particle size distribution that a particle size ofa peak in the distribution is not more than 1.5 μm and the peak of thisdistribution is one.

The roughened surface of the adhesive layer is favorable to have adepression depth Rmax=1-5 μm.

Further, the printed circuit board (multilayered printed wiring board)according to the present invention is characterized by having thefollowing construction.

(3) In the printed circuit board comprising a substrate having formedthereon a conductor circuit, a cured adhesive layer for electrolessplating formed on the substrate by dispersing cured heat-resistant resinparticles soluble in acid or oxidizing agent into uncured heat-resistantresin matrix hardly soluble in acid or oxidizing agent through curingtreatment, a roughened surface formed on the adhesive layer in such amanner that the heat-resistant resin particles are dissolving andremoved, and an upper conductor circuit formed on the roughened surface,

said printed circuit board is characterized in that the adhesive layerfor electroless plating contains more heat-resistant particles at theside of the substrate than that at the opposite side thereof.

Here, it is desirable that the adhesive layer is formed in double-layer,the heat-resistant particles in the adhesive layer at the side of thesubstrate is 20-50% by weight of to a solid content of theheat-resistant resin matrix, while the heat-resistant particles in theadhesive layer at the opposite side of the substrate is not less than 5%by weight but less than 20% by weight of to a solid content of theheat-resistant resin matrix.

Furthermore, material composition for preparing the adhesive for theelectroless plating, according to the present invention, which iscapable of suppressing the curing of the adhesive which inevitablyoccurs in the course of preservation, is comprised of resin compositiongroups 1-3, each of the group prepared in advance for mixture, and keptor preserved in a separated manner to one another;

group 1: a resin composition comprising an uncured thermosetting resinwhich becomes hardly soluble in the acid or oxidizing agent throughcuring treatment,

group 2: a resin composition comprising a cured heat-resistant resinparticles soluble in an acid or oxidizing agent and having an averagepaticle size of not more than 1.5 μm, a thermoplastic resin, and anorganic solvent, and

group 3: a curing agent composition.

Here, it is desirable that the heat-resistant resin particles of thegroup 2 is 5-50% by weight of a solid of the heat-resistant resin matrixin the prepared adhesive agent.

Further, it is desirable that the weight ratio between the thermosettingresin of the group 1 and the thermoplastic resin of the group 2 is¼˜{fraction (4/1)}.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described with reference to the accompanyingdrawings, wherein:

FIGS. 1-20 are diagrammatic views illustrating procsses in theproduction of the multilayer printed circuit board through semi-additiveprocess using the adhesive for electroless plating according to thepresent invention;

FIGS. 21-24 are diagrammatic views illustrating procsses in theproduction of the multilayer printed circuit board through additiveprocess using the adhesive for electroless plating according to thepresent invention;

FIG. 25 is a graph of a particle size distribution showing oneembodiment of a relation between particle size of heat-resistant resinparticle and an existing ratio (existing amount) of heat-resistant resinparticles at this particle size, and

FIG. 26 is a graph of a particle size distribution showing anotherembodiment of a relation between particle size of heat-resistant resinparticle and an existing ratio (existing amount) of heat-resistant resinparticles at this particle size.

In the drawings, the reference numeral 1 indicates a substrate, 2 aninterlaminar resin insulating layer (adhesive layer for electrolesspalting), 3 a permanent resist (plating resist), 4 an inner conductorcircuit (inner layer pattern), 5 an inner conductor circuit (secondlayer pattern), 6 an opening for viahole, 7 a viahole, 8 a copper foil,9 a through hole, 10 a resin filler, 11 a roughened layer, 12 anelectroless plated film, 13 an electrolytic plated film, 14 a solderresist layer, 15 a nickel plating layer, 16 a gold plating layer, and 17a solder body (solder bump).

DETAILED DESCRIPTION OF THE INVENTION

In the semi-additive process, it is necessary to dissolve and remove theelectroless plated film beneath the plating resist as previouslymentioned. Therefore, if the depression of the roughened surface isdeep, the electroless plated film is apt to be left in the depression,which results in the lowering of the insulation resistance value betweenlines. On the other hand, if the depression has a simple shape and isshallow, the peel strength of the plated film lowers and the conductoris apt to be peeled off.

In case of the full-additive process, the palladium catalyst remainsbeneath the plating resist as previously mentioned, so that if thedepression of the roughened surface is deep, the insulation resistancevalue between lines lowers under conditions of high temperature and highhumidity. On the other hand, if the depression has a simple shape and isshallow, the peel strength of the plated film lowers and the conductoris apt to be peeled off likewise the case of the semi-additive process.

In this connection, the adhesive for electroless plating according tothe present invention is characterized by including the heat-resistantresin particles having an average particle size of not more than 1.5 μm,preferably the heat-resistant resin particles having a particle sizedistribution such that the particles do not have a particle size in apeak of this distribution while more than 1.5 μm. As a result, thedepression of the roughened surface is not deep due to the dissolutionof the resin particles having a large particle size (i.e. the depressionof the roughened surface is made shallow) and hence the dissolvedresidue of the electroless plated film in the depression is removed orthe amount of the palladium catalyst beneath the plating resist isdecreased, so that the insulation reliability between lines and betweenlayers can be ensured while maintaining the practical peel strength evenif the roughened surface has shallow depressions.

In the adhesive for electroless plating according to the presentinvention, the heat-resistant resin particles are not more than 1.5 μmin the average particle size, and preferably have a particle sizedistribution such that the particles do not have a particle size in apeak of this distribution which is more than 1.5 μm, so that the depthof the depression formed by removal and dissolution is shallow withoutthe resin particles having a large particle size as in the conventionaltechnique and there is caused no gap even when the roughening tooproceeds. Therefore, the printed circuit board produced by using theadhesive containing such heat-resistant resin particles is excellent inthe insulating property between layers.

In the printed circuit board produced by using the adhesive containingthe heat-resistant resin particles, the practical peel strength can bemaintained even if the depression of the roughened surface is shallow.

For example, in case of the full-additive process, the photosensitiveresin layer for the formation of the plating resist formed on theroughened surface is subjected to light exposure and development to formthe plating resist. Therefore, if the depression of the roughenedsurface is deep, the developed residue of the plating resist is liableto be retained in the depression. In the invention, however, thedepression to be formed is shallow and the resist in the depression caneasily be developed, so that there is hardly created the developedresidue of the plating resist, and even if the depression is madeshallow, the lowering of the peel strength is relatively small.

On the other hand, in case of the semi-additive process, there is amethod of directly forming the electroless plated film on the roughenedsurface, so that the plating resist does not remain in the depression ofthe roughened surface, and even if the depression is made shallow, thelowering of the peel strength is relatively small.

Moreover, when the opening for the formation of the viahole is formed bylight exposure and development, laser processing or the like, theadhesive for electroless plating remains as a residue in the bottom ofthe opening for the formation of the viahole. In the invention, the fineheat-resistant resin particles soluble in acid or oxidizing agent havingan average particle size of not more than 1.5 μm (preferably 0.1-1.0 μm)are existent in the adhesive for electroless plating, so that the aboveresidue can easily be removed by the roughening treatment with acid oroxidizing agent and hence it is not necessary to form a layer for theremoval of the residue beneath the adhesive layer.

In the present invention, the resulting depression is shallow, so thateven when adopting either semi-additive process or full additiveprocess, there can be formed a fine pattern having a ratio of line/space(hereinafter referred to as L/S simply)=less than 40/40 μm.

The heat-resistant resin particles according to the present inventionare preferable to be spherical particles instead of ground particles.Because when the heat-resistant resin particles are ground particles,the depression shape in the roughened surface is sharp and stressconcentration is apt to be caused in the sharped corner and cracks areliable to be created from the corner through heat cycle.

The heat-resistant resin particles are preferred to have an averageparticle size of 0.1-1.0 μm. When the average particle size is withinthe above range, the depth of the depression formed by dissolving andremoving the heat-resistant resin particles is approximately Rmax=about3 μm.

As a result, in the semi-additive process, the electroless plated filmon the non-conductor portion can easily be removed by etching and alsothe Pd catalyst nucleus existing beneath the electroless plated film caneasily be removed, while the peel strength of the conductor portion canbe maintained at a practical level of 1.0-1.3 kg/cm. On the other hand,in the full-additive process, the amount of Pd catalyst nucleus beneaththe plating resist can be decreased and also the plating resist residueon the conductor portion can be removed, so that even if the depressionis shallow, the peel strength can be maintained at a practical level of1.0-1.3 kg/cm.

The heat-resistant resin particles are desirable to have such a particlesize distribution that a peak of this distribution is not more than 1.5μm, preferably 0.1-1.0 μm. Particularly, when the peak of the particlesize distribution is existent in a region of 0.1-1.0 μm, it is desirablethat a standard deviation is not more than 0.5. By the adjustment of theparticle size distribution, the particles constituting theheat-resistant resin particles are less than 2 μm, whereby the influenceof the resin particles having a large particle size as in theconventional technique can completely be eliminated.

In this case, the particle size distribution of the heat-resistant resinparticles is measured by laser diffraction/scattering process. Ameasuring theory of the laser diffraction/scattering process will bedescribed below.

At first, a laser beam is irradiated to the particles to be measured tospacely create a pattern of light intensity distribution of thediffraction/scattering light. The light intensity distribution patternchanges in accordance with the size of the particles. That is, theparticle size and the light intensity distribution pattern are existentas a relation of 1:1, so that the particle size can be specified byproviding the light intensity distribution pattern.

The actual sample is particle groups comprised of many particles.Therefore, light intensity distribution pattern is a piling ofdiffraction/scattering lights of respective particles. Therefore, theparticle size distribution of the sample particle groups is calculatedfrom the piled light intensity distribution patterns.

Moreover, there are Shimazu laser diffraction type particle sizedistribution measuring device SALD-2000/SALD-2000A and Shimazu laserdiffraction type particle size distribution measuring device SALD-3000made by Shimazu Seisakusho as a measuring device utilizing such a laserdiffraction/scattering process.

As the thus obtained particle size distribution, there is a relationbetween the particle size and an existing ratio (existing quantity) ofthe resin particles indicating such a particle size as shown, forexample, in FIGS. 25 and 26. The term peak of particle size distributionused herein means a maximum point of the existing ratio of the resinparticles.

In the present invention, the heat-resistant resin particles arefavorable to have one peak of the particle size distribution. That is,the maxim value of the existing ratio (existing quantity) of the resinparticles is one.

By such a particle size distribution, the light scattering resulted fromthe distribution of the particle size can be controlled and hence thedeveloped residue becomes less. Further, the maintenance of the productis easy and the scattering of the properties such as peel strength andthe like hardly occurs and the printed circuit board can be provided inan excellent mass production.

Moreover, the adjustment of particle size distribution is carried out bycentrifugal separation, air classification, sieving or the like.

In the adhesive for electroless plating according to the presentinvention, the mixing ratio of the heat-resistant resin particles is5-50% by weight, preferably 10-40% by weight to a solid content in theheat-resistant resin matrix as a weight ratio. The reason is that whenthe resin particles are contained too much, the breakage of interlaminarinsulation is apt to be caused due to the progress of the roughening andhence a clear roughened surface can not be formed, while when the resinparticles are contained less, the clear roughened surface can not beformed.

In the adhesive for electroless plating according to the presentinvention, it is necessary that the heat-resistant resin particles arepreviously subjected to a curing treatment. If the particles are notcured, they are dissolved in a solvent dissolving the resin matrix anduniformly mixed with the matrix and hence only the heat-resistant resinparticles can not selectively be dissolved and removed with acid oroxidizing agent.

In the adhesive for electroless plating according to the presentinvention, thermosetting resins (including a case of photosensitizing apart or whole of thermosetting group) and a composite of thermosettingresin (including a case of photosensitizing a part or whole ofthermosetting group) and thermoplastic resin can be used as theheat-resistant resin matrix.

As the thermosetting resin, use may be made of epoxy resin, phenolicresin, polyimide resin and the like. As the epoxy resin, use may be madeof novolac-type epoxy resin, alicyclic epoxy resin and the like.

It is desirable that in the thermosetting resin a part of thethermosetting functional group is replaced with photosensitive group toimpart photosensitivity. This is because if the interlaminar insulatinglayer is formed by using such adhesive agent that contains as a resincomponent the thermosetting resin with photosensitivity, the openingsfor the viaholes may easily be formed in the adhesive layer by the lightexposure and development treatment.

Moreover, if a part or whole of the thermosetting group isphotosensitized, it is acrylated by reacting with methacrylic acid,acrylic acid or the like. Particularly, an acrylated epoxy resin isoptimum.

As the thermoplastic resin, use may be made of polyether sulphone,polysulphone, polyphenylene sulphone, polyphenylene sulfide, polyphenylether, polyether imide and the like.

The thermoplastic resin is preferred to be less than 30% by weight of asolid content in the resin matrix, more preferably 10-25% by weight ofthe solid content in the resin matrix. If it is not less than 30% byweight of the solid content in the resin matrix, the thermoplastic resinremains at the bottom of the opening for the formation of the viahole,resulting in the peeling off between the viaholes and inner conductorcircuits due to bad continuity and heating test.

The heat-resistant resin matrix is preferred to be a composite of theepoxy resin and PES, and PES in the composite is less than 30% by weightof a solid content of the heat-resistant resin matrix.

In the adhesive for electroless plating according to the presentinvention, amino resin (such as melamine resin, urea resin, guanamineresin or the like), epoxy resin, bismaleimide-triazine resin and thelike can be used as a material for the heat-resistant resin particles.

In the adhesive for electroless plating according to the presentinvention, amino resin (such as melamine resin, urea resin, guanamineresin or the like), epoxy resin, bismaleimide -triazine resin and thelike can be used as a material for the heat-resistant resin particles.

Moreover, the epoxy resins can optionally be prepared to ones soluble inacid or oxidizing agent and ones hardly soluble therein by properlyselecting kind of oligomer, kind of curing agent and the like. Forexample, resin obtained by curing bisphenol A-type epoxy oligomer withan amine curing agent is easily soluble in chromic acid, while resinobtained by curing cresol novolac type epoxy oligomer with an imidazolecuring agent is hardly soluble in chromic acid.

Moreover, the adhesive for electroless plating according to the presentinvention may be rendered into B-stage by impregnating in a fibroussubstrate such as glass cloth or the like, or may be shaped into a film.Further, it may be shaped into a substrate. Moreover, the adhesive forelectroless plating according to the present invention may beflame-retarded by halogenating the constitutional resin, or may be addedwith coloring matter, pigment and ultraviolet ray absorbing agent. Andalso, the toughness and thermal expansion coefficient may be adjusted byfilling fibrous filler or inorganic filler.

Then, the printed circuit board using the adhesive for electrolessplating according to the present invention is a printed circuit boardcomprising a substrate, a cured adhesive layer for electroless platinghaving a roughened surface, and a conductor circuit formed on theroughened surface of the adhesive layer, this adhesive layer is composedof an adhesive for electroless plating formed by dispersing curedheat-resistant resin particles soluble in acid or oxidizing agent intouncured heat-resistant resin matrix hardly soluble in acid or oxidizingagent through curing treatment, characterized in that the heat-resistantresin particles have an average particle size of not more than 1.5 μm,preferably 0.1-1.0 μm.

In the printed circuit board according to the present invention, theheat-resistant resin particles are not more than 1.5 μm in the averageparticle size, and preferably have a particle size distribution suchthat the particles do not have a particle size in a peak of thedistribution which is more than 1.5 μm, so that the depth of thedepression formed by removal and dissolution is shallow without theresin particles having a large particle size as in the conventionaltechnique and there is caused no gap even when the roughening tooproceeds. Therefore, the printed circuit board according to the presentinvention having the adhesive containing such heat-resistant resinparticles is excellent in the insulating property between layers.Further, the printed circuit board according to the present inventionmaintain the practical peel strength even when the depression of theroughened surface is shallow.

In the printed circuit board according to the present invention, theheat-resistant resin particles are preferred to have one peak of theparticle size distribution. That is, the maximum value of the existingratio (existing quantity) of the resin particles is one. By such aparticle size distribution, the light scattering resulted from thedistribution of the particle size can be controlled and hence thedeveloped residue becomes less. As a result, the wall face shape in theopening portion for viahole is good.

In the printed circuit board according to the present invention, theroughened surface of the adhesive layer is preferred to have adepression depth of Rmax=1-5 μm. This depression depth is about half ofa depression depth Rmax=10 μm in the roughened surface formed by theconventional adhesive, which is a range of not leaving the plated filmeven if the electroless plated film is dissolved and removed beneath theplating resist and capable of decreasing the amount of the palladiumcatalyst nucleus beneath the playing resist.

Furthermore, it is preferable that the roughened surface has depressiondepth of 1-5 μm and the count value of the peak (Pc) of the roughnessper a 2.5 mm length of the surface, where 0.01≦Pc≦0.1 μm is 10-2500, thecount value where 0.1≦Pc≦1.0 μm is 100-1000, respectively. With suchdecreased number of minute depressions, the plating resist is preventedfrom remaining on the roughened surface in the full-additive process,and the electroless plating film and Pd catalyst are prevented fromremaining on the roughened surface. It has been found that the peelstrength is not reduced with the decreased number of the minutedepressions.

The number of the minute depressions are counted or measured by means ofthe atomic force microscope (AFM by Olympus Optical Co.,Ltd.) in the ACmode operation (resonance) after 10 minutes Blower-type staticelectricity removal operation.

The Japanese unexamined patent publication No.10-4262 discloses suchroughened surface with which conductor circuitry is in contact. Withrespect to such roughened surface, the count value of the peak (Pc) ofthe roughness per a 2.5 mm length of the surface, where 0.01≦Pc≦0.1 μmis 12000 or greater, and the count value of the peak (Pc) where0.1≦Pc≦1.0 μm is 25000 or greater, respectively, however, the number ofthe minute depression is excessive, and the plating resist, electrolesplating film and Pd catalyst remains in the roughened surface, resultingin the peel strength not improved.

In the printed circuit board according to the present inventioncomprising a substrate having formed thereon a conductor circuit, acured adhesive layer for electroless plating formed on the substrate bydispersing cured heat-resistant resin particles soluble in acid oroxidizing agent into uncured heat-resistant resin matrix hardly solublein acid or oxidizing agent through curing treatment, a roughened surfaceformed on the adhesive layer in such a manner that the heat-resistantresin particles are dissolving and removed, and an upper conductorcircuit formed on the roughened surface, the printed circuit board ischaracterized in that the adhesive layer for electroless platingcontains more heat-resistant particles at the side of the substrate thanthat at the opposite side thereof.

According to such structure of the interlaminar insulating resin layer,it is possible to realize shallow roughened surfaces with high roughingability, providing a multilayered printed circuit board having finepatterns and minute viaholes.

In concrete, it is desirable that the adhesive layer is formed indouble-layer (underlayer and upperlayer), the heat-resistant particlesin the adhesive layer at the side of the substrate (upperlayer) is20-50% by weight of a solid content of the heat-resistant resin matrix,while the heat-resistant particles in the adhesive layer at the oppositeside of the substrate (upper layer) is not less than 5% by weight butless than 20% by weight of a solid content of the heat-resistant resinmatrix.

The compounding quantity of the heat-resistant resin particles containedin the underlayer of the adhesive layer is selected to be within such arange that the resin residue may be removed in the roughening treatmentand the inner wall of the bottom of the viahole does not become solarge, while the compounding quantity of the heat-reistant resinparticles contained in the upperlayer of the adhesive layer is selectedto be within such a range that the anchoring of the roughened surfacemay be shallow enough to obtain an adequate peel strength.

In this invention, the adhesive layer is desirable to have a thicknessof less than 50 μm, preferably 15-45 μm. If the thickness is less than50 μm, the heat-resistant resin particles in the adhesive layer are aptto be associated to one another, causing breakage of the interlaminarinsulating. In this connection, according to the present invention, suchbreakage is not easily occurred due to the minute diameter of theheat-resistant resin particles.

Further, it is desirable that viaholes each having a diameter of lessthan 100 μm are formed on the adhesive layer for the electrolessplating. In the case of forming viaholes having smaller diameter,developed residue of the plating resist is liable to be retained. Inthis connection, the developed residue can easily be removed since theadhesive agent containing the minute heat-resistant resin particles isused in the present invention. Further, in the case of forming viaholeswith smaller diameter, when the adhesive agent contains larger-sizeparticles, the viahole diameter becomes large in the rougheningtreatment. In this connection, it is advantageous to use such adhesiveagent containing minute heat-resistant resin particles.

In the printed circuit board according to the present invention, theconductor circuit formed on the roughened surface of the adhesive layeris preferable to be comprised of thin electroless plated film and thickelectrolytic plated film in the semi-additive process. Since theelectrolytic plated film showing a small plating stress is thickened,even if the depression of the roughened surface is shallow, there iscaused no peeling of the plated film.

In the printed circuit board according to the present invention, theconductor circuit may be formed on the surface of the substrate formingthe adhesive for electroless plating thereon. In this case, theconductor circuit is preferred to have a roughened layer on at least apart of the surface thereof. For example, it is desirable that when thesubstrata is formed through the full-additive process, the rougheninglayer is formed on an upper surface of the conductor circuit, or whenthe substrate is formed through the semi-additive process, the roughenedlayer is formed on a aide surface or full surface of the conductorcircuit. Because the adhesion property to the adhesive layer forelectroless plating is improved by these roughening layers and hence theoccurrence of cracks resulted from the difference of thermal expansioncoefficient between the conductor circuit and the adhesive forelectroless plating in the heat cycle can be controlled.

Further, it is preferred that the roughened layer is formed on at leasta part of the surface of the conductor circuit formed on the roughenedsurface of the adhesive layer, i.e. an upper surface, side surface orfull surface thereof. Because, the adhesion property to a solder resistcovering the conductor circuit or an upper interlaminar insulating resinlayer can be improved to control the occurrence of cracks in the heatcycle.

The formation of such roughened surface is apt to cause the resinremained in the roughened layer when the opening for the formation ofviaholes are formed in the upper interlaminar insulating resin layer. Inthis connection, according to the adhesive for electroless platingcomprising fine particles having an average particle size of not morethan 2 μm as heat-resistant resin particles soluble in an acid oroxidizing agent, the resin residue can easily be dissolved and removedby the acid or oxidation treatment, since such fine particles arepresent in the resin residue in the roughened surface.

The roughness of the roughened surface is preferred to be 0.1 μm˜10 μm,because this range of roughness provides best adhesion property.

It is desirable that the roughness of the roughened surface is 0.1˜10 μmand the count value of the peak (Pc) of the roughness at a surfacelength of 2.5 mm where 0.01≦Pc≦0.1 μm is 100˜1000, the count value where0.1≦Pc≦1.0 μm is 100˜2000, respectively. With such comparativelydecreased number of minute depressions, the resin residue in theroughened surface appearing when the openings for the formation ofviaoles are formed can be reduced. Further, with such decreased numberof minute depressions that do not improve the peel strength, the highfrequency signal is prevented from being delayed in propagation alongthe conductor circuit, since the high frequency signal travels on asurface of the conductor layer.

The Japanese unexamined patent publication No. 10-4261 discloses suchroughened surface with which conductor circuitry is in contact that thecount value of the peak (Pc) of the roughness per a 2.5 mm length of thesurface, where 0.01≦Pc≦0.1 μm is 30000 or greater, and the count valueof the peak (Pc) where 0.1≦Pc≦1.0 μm is 3000-10000, respectively,however, the number of the minute depression is excessive, and the resinresidue can remarkably be seen.

The number of the minute depressions was counted or measured by means ofthe atomic force microscope (AFM by Olympus Optical Co., Ltd.) in the ACmode operation (resonance) after 10 minutes Blower-type staticelectricity removal operation.

Next, the material composition for preparing the above-mentionedadhesive for electroless plating will be explained.

The material composition is comprised of resin composition groups 1-3,each group prepared in advance for mixture, and kept or preserved in aseparated manner to one another;

group 1: a resin composition comprising an uncured thermosetting resinwhich becomes hardly soluble in the acid or oxidizing agent throughcuring treatment,

group 2: a resin composition comprising a cured heat-resistant resinparticles soluble in an acid or oxidizing agent and having an averageparticle size of not more than 1.5 μm, a thermoplastic resin, and anorganic solvent, and

group 3: a curing agent composition.

With each resin composition of each group being kept or preserved in aseparated manner to one another, the curing of the resin component ofeach composition does not proceed, and there can be seen no viscosityincreasing. If the resin compositions of group 1 and 2 are mixedtogether and left as it is for a long time, the mixture is get gelationand the viscosity increases despite of the absence of the curing agent.In this connection, such gelation does not occur because the compositionof each group is preserved in a separated manner to one another.

Further, according to the present invention, the photo-polymerizationreaction of the resin component does not proceed even in the case of theresin component exposed to light. As a result, no degradation can beseen in the resolving degree when the adhesive for electroless platingcomprising such material composition is applied on the substrate andexposed to light in the manufacturing process of the printed circuitboard.

In the material composition of the present invention, it is desirablethat a mixing ratio of the heat-resistant resin particles is 5-50% byweight of a solid content of the heat-resistant resin matrix in theprepared adhesive agent, as a weight ratio.

Furthermore, a mixing ratio of the thermosetting resin in the group 1 tothe thermoplastic resin in the group 2 is preferable to be ¼˜{fraction(4/1)} as a weight ratio. This is because such a range of the mixingratio can provide an improved toughness of the thermosetting resin.

The organic solvent in the group 2 is preferable to be 100-300 parts byweight of the 100 parts of the thermoplastic resin.

The curing agent in the group 3 is preferable to be 1-10% by weight of atotal solid content of the adhesive for electroless plating matrix.

As the curing agent, it is desirable to use such a type of curing agentthat is liquid at the temperature of 25° C., i.e. liquid imidazolecuring agent such as 1-benzyl-2-ethylimidazole(1B2MZ),1-cyanoethyl-2-4-methylimidazole (2E4MZ-CN), or4-methyl-2-ethylimidazole (2E4MZ).

As the organic solvent, it is desirable to use glycolic ether typesolvent such as diethylene glycol dimethyl ether (DMDG), and triethyleneglycol dimethyl ether (DMTG), having the below structural formulatornormal methyl pyroridone (NMP).

CH₃O—(CH₂CH₂O)_(n)—CH₃ (n=1˜5)

A photosensitive monomer and/or deforming agent may be added to thecomposition of the group 1. As the photosensitive monomer, Aronix M325,M315 (by Toa Gosei Co., Ltd.), DPE-6A (by Nippon Kayaku Co., Ltd.), orR-604(by Kyoeisha Kagaku Co., Ltd) may be used. As the deforming agent,silicon type deforming agent or S-65 (by Sannopco Co., Ltd.) may beused.

It is desirable that the composition of the group 3 contains a curingagent of the thermosetting resin and photoinitiator, ensuring thecarrying out of exposure and development treatment of the adhesive andcuring of the adhesive by heating treatment. Further, photoinitiator andphotosensitizer may be added to the composition of the group 3.

As the photoinitiator, Irgaquar 907 made by Ciba Geigy or benzophenonemay be used, and as the photosensitizer, DETX-S made by Nippon kayakuCo., Ltd. or Michelars' ketone may be used.

A method of producing the printed circuit board according to the presentinvention through semi-additive or full-additive process will concretelybe described below.

[Semi-Additive Process]

(1) In order to produce a multilayer circuit board through thesemi-additive process, a circuit substrate is first prepared by forminga conductor circuit on a surface of a substrate.

As the substrate, use may be made of insulating resin substrates such asglass epoxy substrate, polyimide substrate, bismaleimide-triazinesubstrate and the like, ceramic substrate, metal substrate and so on.

The conductor circuit in the wiring substrate is formed by a method ofetching a copper-clad laminate, or a method of forming an adhesive layerfor electroless plating on a substrate such as glass epoxy substrate,polyimide substrate, ceramic substrate, metal substrate or the like androughening the surface of the adhesive layer and subjecting theroughened surface to an electroless plating, or so-called semi-additiveprocess (the whole of the roughened surface is subjected to a thinelectroless plating to form a plating resist and a portion not formingthe plating resist is subjected to thick electrolytic plating and theplating resist is removed and etched to form a conductor circuitcomprised of the electrolytic plated film and electroless plated film).

Moreover, the conductor circuit in the wiring substrate can improve theadhesion property to the interlaminar insulating resin layer to beformed on the conductor circuit by forming a roughened layer consistingof copper-nickel-phosphorus on the surface inclusive of at least a sidesurface.

The roughened layer is preferred to be formed by the electrolessplating. The composition of the electroless plating solution isdesirable to have a copper ion concentration of 2.2×10⁻²-4.1×10⁻² mol/l,a nickel ion concentration of 2.2×10⁻³-4.1×10⁻³ mol/l and ahypophosphorous acid ion concentration of 0.20-0.25 mol/l, respectively.The film precipitated within the above range is needle in the crystalstructure and is excellent in the anchor effect. Moreover, a complexingagent and additives may be added to the electroless plating bath inaddition to the above compounds.

As the other method of forming the roughening layer, there is a methodof subjecting the surface of the conductor circuit to oxidation(graphitization)-reduction, etching treatment or the like.

The roughened layer may be covered with a layer of metal or noble metalhaving an ionization tendency of more than copper but less thantitanium. Such a metal or noble metal layer covering the roughened layercan prevent the dissolution of the conductor circuit due to a localelectrode reaction created in the roughening of the interlaminarinsulating resin layer. The thickness of this layer is 0.1-2 μm.

As the metal, there is at least one metal selected from titanium,aluminum, zinc, iron, indium, thallium, cobalt, nickel, tin, lead,bismuth and the like. As the noble metal, there are gold, silver,platinum and palladium. Among them, tin is preferable. Tin can form athin layer through electroless substitution plating and canadvantageously be followed to the roughened layer. In case of tin, asolution of tin borofluoride-thiourea or tin chloride-thiourea is used.In this case, Sn layer having a thickness of 0.1-2 μm is formed throughCu—Sn substitution reaction. In case of the noble metal, there areadopted sputtering method, vaporization method and the like.

In the core substrate are formed through-holes, and front wiring layerand back wiring layer are electrically connected to each other throughthe through-holes.

Further, a low viscosity resin such as bisphenol F-type epoxy resin orthe like is filled in the through-hole and between the conductorcircuits of the core substrate to ensure the smoothness of the wiringsubstrate.

(2) Then, an interlaminar resin insulating agent is applied to thewiring substrate prepared in the step (1).

As the interlaminar resin insulating agent is used the adhesive forelectroless plating according to the present invention. In this case,roll coater, curtain coater and the like can be used for the applicationof the interlaminar resin insulating agent.

Moreover, in case of plural interlaminar insulating resin layers, theparticle size of the heat-resistant resin particles in each of thelayers may be changed. For example, the heat-resistant resin particlesof the underlayer have an average particle size of 0.5 μm, and theheat-resistant resin particles of the upperlayer have an averageparticle sizes of 1.0 μm, whereby the adhesive for electroless platingmay be constructed with heat-resistant resin particles having differentparticle sizes. Particularly, the heat-resistant resin particles of theunderlayer have an average particle size of 0.1-2.0 μm, more preferably0.1-1.0 μm.

Specifically, the material composition for the preparation of theadhesive for electroless plating according to the present invention maybe mixed together just before applying and then applied as the adhesivefor electroless plating.

Such adhesive for electroless plating is prepared by mixing thecomponents of the material composition by means of roll kneading, ballmills or bees mills. For example, firstly, the components of the group 2are mixed together and adjusted by means of roll kneading, ball mills orbees mills, and after mixing the components, the components of the group1 and the curing agent of the group 3 are added to the mixture and mixedall together.

As the heat-resistant resin matric constituting the adhesive layer ofthe underlayer, there can be used a thermosetting resin, a thermosettingresin (a part or whole of thermosetting group is photosensitized), or acomposite of thermosetting resin (a part or while of thermosetting groupis photosensitized) and thermoplastic resin.

As the thermosetting resin constituting the adhesive layer of theunderlayer, there can be used epoxy resin, phenolic resin, polyimideresin and the like. When a part of the thermosetting group isphotosensitized, a part of the thermosetting group is acrylated byreacting with methacrylic acid, acrylic acid or the like. Among them,acrylated epoxy resin is optimum. As the epoxy resin, there can be usednovolac type epoxy resin, alycyclic epoxy resin and the like.

As the thermoplastic resin constituting the adhesive layer of theunderlayer, use may be made of polyether sulphone, polysulphone,polyphenylene sulphone, polyphenylene sulfide, polyphenyl ether,polyether imide and the like.

As the heat-resistant resin particle constituting the adhesive layer ofthe underlayer, use may be made of amino resin (melamine resin, urearesin, guanamine resin and the like), epoxy resin, bismaleimide-triazineresin and the like.

(3) The applied interlaminar resin insulating agent is dried.

At this time, the interlaminar insulating resin layer formed on theconductor circuit of the substrate has frequently a state of causingunevenness due to the fact that the thickness of the interlaminarinsulating resin layer on the conductor circuit pattern is thin and thethickness of the interlaminar insulating resin layer on the conductorcircuit having a large area is thick. Therefore, it is desirable thatthe surface of the interlaminar insulating resin layer is smoothened bypushing a metal plate or a metal roll onto the interlaminar insulatingresin layer of the uneven state while heating.

(4) Next, an opening for the formation of viahole is formed in theinterlaminar insulating resin layer while curing the interlaminarinsulating resin layer.

The curing treatment of the interlaminar insulating resin layer iscarried out by heat-curing when the resin matrix of the adhesive forelectroless plating is a thermosetting resin, or by exposing to anultraviolet ray or the like when it is a photosensitive resin.

The opening for the formation of viahole formed by using a laser beam oran oxygen plasma when the resin matrix of the adhesive for electrolessplating is a thermosetting resin, or by light exposure and developmentwhen it is a photosensitive resin. Moreover, the light exposure anddevelopment are carried out after a photomask depicted with a circlepattern for the formation of the viahole (glass plate is favorable) isclosely placed on the photosensitive interlaminar insulating resin layerso as to face the side of the circle pattern to the layer.

(5) The surface of the interlaminar insulating resin layer (adhesive forelectroless plating) provided with the opening for the formation of theviahole is roughened.

In the present invention, the surface of the adhesive layer isparticularly subjected to a roughening treatment by dissolving andremoving the heat-resistant resin particles existing in the surface ofthe adhesive layer for electroless plating with acid or oxidizing agent.In this case, the depression depth of the roughened surface is preferredto be about 1-5 μm.

As the acid, there are phosphoric acid, hydrochloric acid, sulfuric acidand organic acids such as formic acid, acetic acid and the like.Particularly, the use of the organic acid is desirable. Because, ithardly corrodes the metal conductor layer exposed from the viahole inthe roughening treatment.

As the oxidizing agent, it is desirable to use chromic acid, orpermanganate (potassium permanganate or the like).

(6) Next, a catalyst nucleus is applied to the roughened surface of theinterlaminar insulating resin layer.

In the application of the catalyst nucleus, it is desired to use a noblemetal ion, a noble metal colloid or the like. In general, palladiumchloride or palladium colloid is used. Moreover, it is desired toconduct a heating treatment for fixing the catalyst nucleus. As thecatalyst nucleus, palladium is favorable.

(7) An electroless plated film is thinly formed on the full roughenedsurface of the interlaminar insulating resin layer.

As the electroless plated film, an electroless copper plated film isfavorable and has a thickness of 1-5 μm, more particularly 2-3 μm. Asthe electroless copper plating solution, use may be made of any solutioncomposition used in the usual manner. For example, a solutioncomposition comprising copper sulfate: 29 g/l, sodium carbonate: 25 g/l,tartarate: 140 g/l, sodium hydroxide: 40 g/l, and 37% formaldehyde: 150ml (pH=11.5).

(8) A photosensitive resin film (dry film) is laminated on theelectroless plated film formed in the step (7) and a photomask (glasssubstrate is preferred) depicted with a plating resist pattern isclosely placed thereonto, which is subjected to a light exposure anddevelopment to form a non-conductor portion forming the plating resistpattern.

(9) An electrolytic plated film is formed on the electroless plated filmother than the non-conductor portion to form conductor circuits andconductor portion as a viahole.

As the electrolytic plating, it is desirable to use an electrolyticcopper plating, and the thickness thereof is favorably 10-20 μm.

(10) After the plating resist on the non-conductor portion is removed,the electroless plated film is removed by dissolving in an etchingsolution such as a mixture of sulfuric acid and hydrogen peroxide,sodium persulfate, ammonium persulfate, iron chloride, copper chlorideor the like to obtain independent conductor circuits consisting of theelectroless plated film and the electrolytic plated film and viaholes.Moreover, the palladium catalyst nucleus on the roughened surfaceexposed from the non-conductor portion is dissolved and removed bychromic acid or the like.

(11) A roughened layer is formed on the surface of the conductor circuitand viahole formed in the step (10).

As the method of forming the roughened layer, there are etchingtreatment, polishing treatment, redox treatment or plating treatment.

The redox treatment is conducted by using an oxidation bath(graphitization bath) of NaOH (10 g/l), NaClO₂ (40 g/l) and Na₃PO₄ (6g/l) and a reduction bath of NaOH (10 g/l) and NaBH₄ (5 g/l).

Furthermore, when the roughened layer is made fromcopper-nickel-phosphorus alloy layer, it is precipitated by theelectroless plating. As the electroless alloy plating solution, it isfavorable to use a plating bath of solution composition comprisingcopper sulfate: 1-40 g/l, nickel sulfate: 0.1-6.0 g/l, citric acid:10-20 g/l, hypophosphite: 10-100 g/l, boric acid: 10-40 g/l andsurfactant: 0.01-10 g/l.

(12) An interlaminar insulating resin layer is formed on the substrateaccording to the steps (2), (3).

(13) If necessary, the formation of multilayer is carried out byrepeating the steps (4)-(10) to produce a multilayer circuit board.

[Full-Additive Process]

(1) The aforementioned steps (1)-(6) are carried out by using theadhesive for electroless plating according to the invention likewise thesemi-additive process.

(2) A non-conductor portion forming the plating resist pattern is formedon the roughened surface of the interlaminar insulating resin layer(adhesive layer for electroless plating) provided with the catalystnucleus.

The plating resist is formed by laminating a commercially availablephotosensitive dry film and subjecting to light exposure anddevelopment, or by applying a liquid plating resist composition with aroll coater or the like, drying, and subjecting to light exposure anddevelopment.

As the plating resist composition, it is desirable to use aphotosensitive resin composition comprising a resin obtained byacrylating a novolac type epoxy resin such as cresol novolac type epoxyresin, phenol novolac type epoxy resin or the like with methacrylic acidor acrylic acid and an imidazole curing agent. Because, such aphotosensitive resin composition is excellent in the resolution andresistance to base.

(3) An electroless plating is carried out on portions other than thenon-conductor portion (plating resist portion) to form conductor circuitand conductor portion as a viahole. As the electroless plating, anelectroless copper plating is favorable.

Moreover, when the opening for the formation of the viahole is filled byelectroless plating to form so-called filled viahole, the surface of theconductor layer as an underlayer exposed from the opening for theformation of the viahole is first activated with acid before thecatalyst nucleus is applied to the adhesive layer for electrolessplating, which is immersed in an electroless plating solution. After theopening for the formation of viahole is filled by electroless plating,the catalyst nucleus is given to the adhesive layer for electrolessplating and the plating resist is formed, which is subjected to anelectroless plating to form a conductor layer.

The viahole formed by filling with the electroless plated film can formanother viahole just thereabove, so that it is possible to make a sizeof a circuit board small and a density thereof high.

As means for improving the adhesion force between the conductor layerand the adhesive layer for electroless plating, there is a methodwherein an alloy plating using at least two metal ions selected fromcopper, nickel, cobalt and phosphorus is applied as a primary platingand thereafter copper plating is applied as a secondary plating. Thesealloys are high in the strength and can improve the peel strength.

(4) A roughened layer is formed on upper surfaces of the conductorcircuit formed other than the plating resist portion and the viaholes.

As the method for the formation of the roughened layer, there areetching treatment, polishing treatment, redox treatment and platingtreatment.

Moreover, the roughened layer comprised of copper-nickel-phosphorusalloy layer is formed by precipitation through electroless plating.

(5) If necessary, interlaminar insulating layer as an upperlayer(adhesive layer for electroless plating) and conductor circuit arelaminated to produce a multilayer circuit.

EXAMPLE 1

Semi-Additive Process: 0.5 μm

(1) As a starting material, there is used a copper-clad laminate formedby laminating copper foils 8 of 18 μm onto both surfaces of a substrate1 made from glass epoxy resin or BT (bismaleimide triazine) resin of 0.6mm in thickness (see FIG. 1). At first, the copper-clad laminate isdrilled and subjected to electroless plating and etched in a shape ofpattern to form innerlayer conductor circuits 4 and a through-hole 9 onboth surfaces of the substrate 1.

The surfaces of the innerlayer conductor circuits 4 and through-hole 9are roughened by oxidation (graphitization)—reduction treatment (seeFIG. 2), and bisphenol F-type epoxy resin as a filling resin 10 isfilled between the conductor circuits and in the through-hole (see FIG.3), and thereafter the surface of the substrate is smoothened bypolishing so as to expose the surfaces of the conductor circuits and theland face of the through-hole (see FIG. 4).

(2) After the substrate subjected to the treatment of the step (1) iswashed with water and dried, it is acidically degreased, soft-etched andtreated with a catalyst solution of palladium chloride and organic acidto give a Pd catalyst. After the activation of the catalyst, it issubjected to a plating in an electroless plating bath containing 8 g/lof copper sulfate, 0.6 g/l of nickel sulfate, 15 g/l of citric acid, 29g/l of sodium hypophosphite, 31 g/l of boric acid and 0.1 g/l ofsurfactant and having pH=9 to form a roughened layer 11 (uneven layer)of Cu—Ni—P alloy of 2.5 μm in thickness on the exposed surface of thecopper conductor circuit.

Further, the substrate is immersed in an electroless tin substitutionplating bath containing 0.1 mol/l of tin borofluoride and 1.0 mol/l ofthiourea at 50° C. for 1 hour to form a tin substitution plated layer of0.3 μm in thickness on the surface of the roughened layer 11 (see FIG.5, provided that the tin layer is not shown).

(3) A photosensitive adhesive solution for electroless plating(interlaminar resin insulating agent) is prepared by mixing 34 parts byweight of 25% acrylated product of cresol novolac type epoxy resin (madeby Nippon Kayaku Co., Ltd.; molecular weight: 2500) dissolved in DMDG(diethylene glycol dimethyl ether), 12 parts by weight of polyethersulphone (PES), 2 parts by weight of imidazole curing agent (made byShikoku Kasei Co., Ltd.; trade name: 2E4MZ-CN), 4 parts by weight ofcaprolactone modified tris(acroxyethyl) isocyanurate (made by Toa GoseiCo., Ltd.; trade name: Aronix M315) as a photosensitive monomer, 2 partsby weight of a photoinitiator (made by Ciba Geigy, trade name: Irgaquar907), 0.2 part by weight of a photosensitizer (made by Nippon KayakuCo., Ltd.; trade name: DETX-S) and 25 parts by weight of epoxy resinparticles (made by Sanyo Kasei Co., Ltd.; trade name: Polymerpole. Theparticle size distribution of these particles is shown in FIG. 25. Anaverage particle size of these particles is 0.51 μm as a median size andhas a standard deviation of 0.193. These particles are distributedwithin a range of 0.09-1.32 μm and a particle size in a peak of theparticle size distribution is 0.58 μm and the peak is one as seen fromFIG. 25. Moreover, the measurement of the particle size distribution iscarried out by using Shimazu laser diffraction type particle sizedistribution measuring device SALD-2000 made by Shimazu Seisakusho.),adding with 30.0 parts by weight of NMP (normal methyl pyrolidone),adjusting a viscosity to 7 Pa·s in a homodisper agitating machine andthen kneading through three rolls.

(4) The photosensitive adhesive solution obtained in the step (3) isapplied onto both surfaces of the substrate treated in the step (2) bymeans of a roll coater and left to stand at horizontal state for 20minutes and dried at 60° C. for 30 minutes to form an adhesive layer 2of 60 μm (see FIG. 6(a)).

(5) A polyethylene terephthalate film (light permeation film) isattached to each surface of the adhesive layers 2 formed on bothsurfaces of the substrate in the step (4) through a tackifier. Then, asodalime glass substrate of 5 mm in thickness depicted with the samecircle pattern (mask pattern) as the viahole through a light screen inkof 5 μm in thickness is closely placed on the adhesive layer 2 so as toface the circle pattern depicted side thereto and exposed to anultraviolet ray.

(6) The light-exposed substrate is developed by spraying a DMTG(triethylene glycol dimethyl ether) solution to form openings forviahole of 100 μmφ on the adhesive layer 2. Further, the substrate isexposed to a super-high pressure mercury lamp at 3000 mJ/cm² and heatedat 100° C. for 1 hour and at 150° C. for 5 hours to form an adhesivelayer 2 of 50 μm in thickness provided with openings 6 (opening for theformation of viahole) having excellent dimensional accuracycorresponding to the photomask film. Moreover, the roughened layer 11 ispartly exposed in the opening 6 for the viahole (see FIG. 7).

(7) The substrate having the openings 6 for the formation of viahole inthe steps (5),(6) is immersed in chromic acid for 2 minutes to dissolveand remove epoxy resin particles existing in the surface area of theadhesive layer 2, whereby the surface of the adhesive layer 2 isroughened and then immersed in a neutral solution (made by Shipley) andwashed with water (see FIG. 8).

(8) A catalyst nucleus is applied to the surfaces of the adhesive layer2 and the opening 6 for the formation of viahole by giving a palladiumcatalyst (made by Atotech Co., Ltd.) To the substrate roughened in thestep (7) (roughened depth: 5 μm).

(9) The substrate is immersed in an electroless copper plating bathhaving the following composition to form an electroless copper platedfilm 12 of 3 μm in thickness over a full roughened surface (see FIG. 9).

[Electroless plating solution] EDTA 150 g/l Copper sulfate 20 g/l HCHO30 ml/l NaOH 49 g/l α,α′-bipyridyl 80 mg/l PEG 0.1 g/l

[Electroless Plating Condition]

at a liquid temperature of 70° C. for 30 minutes

(10) A commercially available photosensitive resin film (dry film) isadhered to the electroless copper plated film 12 formed in the step (9)through thermal press and further sodalime glass substrate of 5 mm inthickness depicted with a mask pattern as a portion not forming theplating resist through chromium layer is closely placed onto the dryfilm so as to face the chromium layer side to the dry film, exposed to alight at 110 mJ/cm² and developed with 0.8% sodium carbonate to form apattern of plating resist 3 having a thickness of 15 μm (FIG. 10).

(11) Then, the portion not forming the plating resist is subjected to anelectrolytic copper plating under the following conditions to form anelectrolytic copper plated film 13 having a thickness of 15 μm (see FIG.11).

[Electrolytic plating solution] sulfuric acid 180 g/l copper sulfate 80g/l additive (made by Atoteck Japan, trade name: 1 ml/l Capalacid GL)

[Electrolytic plating solution] current density  1.2 A/dm² time 30minutes temperature Room temperature

(12) After the plating resist 3 is peeled off by spraying 5% KOH, theelectroless plated film 12 located beneath the plating resist 3 isdissolved and removed by etching with a mixed solution of sulfuric acidand hydrogen peroxide to form an innerlayer conductor circuit 5consisting of the electroless copper plated film 12 and the electrolyticcopper plated film 13 and having a thickness of 18 μm. Further, Pdretained in the roughened surface 11 is removed by immersing in chromicacid (800 g/l) for 1-2 minutes (see FIG. 12).

(13) The substrate provided with the conductor circuit 5 is immersed inan electroless plating solution of pH=9 containing 8 g/l of coppersulfate, 0.6 g/l of nickel sulfate, 15 g/l of citric acid, 29 g/l ofsodium hypophosphite, 31 g/l of boric acid and 0.1 g/l of surfactant toform a roughened layer 11 of copper-nickel-phosphorus having a thicknessof 3 μm on the surface of the conductor circuit 5. In this case, theroughened layer 11 has a composition ratio of Cu: 98 mol %, Ni: 1.5% andP: 0.5 mol % as analyzed by EPMA (fluorescent X-ray analyzing device).

Further, the substrate is washed with water and immersed in anelectroless tin substitution plating bath containing 0.1 mol/l of tinborofluoride and 1.0 mol/l of thiourea at 50° C. for 1 hour to form atin substitution plated layer of 0.3 μm on the surface of the roughenedlayer 11 (see FIG. 13 provided that tin substituted layer is not shown).

(14) An adhesive layer 2 is further formed according to the step (4) anda polyethylene terephthalate film (light permeation film) is attached tothe surface thereof, which is sandwiched between stainless plates andheat-pressed by heating in a heating furnace at 65° C. whilepressurizing at 20 kgf/cm². By such a heat pressing is smoothened thesurface of the adhesive layer 2 to form an interlaminar insulating resinlayer (see FIG. 14).

(15) Further, conductor circuits are formed by repeating the steps(5)-(13) and a roughened layer 11 of copper-nickel-phosphorus is formedon the surface of the conductor circuit. In this case, the tinsubstitution plated layer is not formed on the surface of the roughenedlayer (see FIGS. 15-19).

(16) On the other hand, a solder resist composition is prepared bymixing 46.67 parts by weight of a photosensitized oligomer (molecularweight: 4000) obtained by acrylating 50% of epoxy group of 60% by weightof creasol novolac type epoxy resin (made by Nippon Kayaku Co., Ltd.)dissolved in DMDG, 15.0 parts by weight of 80% by weight of bisphenolA-type epoxy resin (made by Yuka Shell Co., Ltd.; trade name: Epikote1001) dissolved in methyl ethyl ketone, 1.6 parts by weight of imidazolecuring agent (made by Shikoku Kasei Co., Ltd.; trade name: 2E4MZ-CN), 3parts by weight of polyvalent acrylmonomer (made by Nippon Kayaku Co.,Ltd.; trade name: R604) as a photosensitive monomer, 1.5 parts by weightof a polyvalent acrylmonomer (made by Kyoeisha Kagaku Co., Ltd.; tradename: DPE6A) and 0.71 part by weight of a dispersion anti-foamer, adding2 parts by weight of benzophenone (made by Kanto Kagaku Co., Ltd.) as aphotoinitiator and 0.2 part by weight of Michler s ketone (made by KantoKagaku Co., Ltd.) as a photosensitizer to the mixture and adjusting aviscosity to 2.0 Pa·s at 25° C.

Moreover, the measurement of the viscosity is carried out by B-typeviscosity meter (made by Tokyo Keiki Co., Ltd.; DVL-B model) accordingto rotor No. 4 at 60 rpm and rotor No. 3 at 6 rpm.

(17) The above solder resist composition is applied to both surfaces ofthe substrate obtained in the step (15) at a thickness of 20 μm. Then,it is dried at 70° C. for 20 minutes and at 70° C. for 30 minutes andthereafter a sodalime glass substrate of 5 mm in thickness depicted withcircle patter (mask pattern) for solder resist opening through chromiumlayer is closely placed on the solder resist layer so as to face thechromium layer side thereto, exposed to an ultraviolet ray at 1000mJ/cm² and developed with DMTG.

Further, it is heated at 80° C. for 1 hour, at 100° C. for 1 hour, at120° C. for 1 hour and at 150° C. for 3 hours to form a pattern ofsolder resist layer 14 (thickness: 20 μm) opening in the upper surfaceof the solder pad, viahole and its land portion (opening size: 200 μm).

(19) The substrate provided with the solder resist layer 14 is immersedin an electroless nickel plating solution of pH=5 containing 30 g/l ofnickel chloride, 10 g/l of sodium hypophosphite and 10 g/l of sodiumcitrate to form a nickel plated layer 15 of 5 μm in the opening.Further, the substrate is immersed in an electroless gold platingsolution containing 2 g/l of potassium gold cyanide, 75 g/l of ammoniumchloride, 50 g/l of sodium citrate and 10 g/l of sodium hypophosphite at93° C. for 23 seconds to form a gold plated layer 16 of 0.03 μm on thenickel plated layer 15.

(20) A solder paste is printed on the opening of the solder resist layer14 and reflowed at 200° C. to form a solder bump (solder body) 17,whereby there is produced a printed circuit board having solder bumps(see FIG. 20).

EXAMPLE 2

Semi-Additive Process: 0.92 μm

A printed circuit board having solder bumps is produced in the samemanner as in Example 1 except that the following adhesive solution forelectroless plating is used.

That is, a photosensitive adhesive solution for electroless plating(interlaminar resin insulating agent) is prepared by mixing 34 parts byweight of 25% acrylated product of cresol novolac type epoxy resin (madeby Nippon Kayaku Co., Ltd.; molecular weight: 2500) dissolved in DMDG(diethylene glycol dimethyl ether), 12 parts by weight of polyethersulphone (PES), 2 parts by weight of imidazole curing agent (made byShikoku Kasei Co., Ltd.; trade name: 2E4M-CN), 4 parts by weight ofcaprolactone modified tris (acroxyethyl) isocyanurate (made by Toa GoseiCo., Ltd.; trade name: Aronix M315) as a photosensitive monomer, 2 partsby weight of a photoinitiator (made by Ciba Geigy, trade name: Irgaquar907), 0.2 part by weight of a photosensitizer (made by Nippon KayakuCo., Ltd.; trade name: DETX-S) and 25 parts by weight of epoxy resinparticles (made by Sanyo Kasei Co., Ltd.; trade name: PolymerpoleSS-001. The particle size distribution of these particles is shown inFIG. 26. An average particle size of these particles is 0.92 μm as amedian size and has a standard deviation of 0.275. These particles aredistributed within a range of 0.10-1.98 μm and a particle size in a peakof the particle size distribution is 1.00 μm and the peak is one as seenfrom FIG. 26. Moreover, the measurement of the particle sizedistribution is carried to by using Shimazu laser diffraction typeparticle size distribution measuring device SALD-2000 made by ShimazuSeisakusho.), adding with 30.0 parts by weight of NMP (normal methylpyrolidone), adjusting a viscosity to 7 Pa·s in a homodisper agitatingmachine and then kneading through three rolls.

EXAMPLE 3

Full-Additive Process

(1) A photosensitive adhesive solution for electroless plating(interlaminar resin insulating agent) is prepared by mixing 34 parts byweight of 25% acrylated product of cresol novolac type epoxy resin (madeby Nippon Kayaku Co., Ltd.; molecular weight: 2500) dissolved in DMDG(diethylene glycol dimethy ether), 12 parts by weight of polyethersulphone (PES), 2 parts by weight of imidazole curing agent (made byShikoku Kasei Co., Ltd.; trade name: 2E4MZ-CN), 4 parts by weight ofcaprolactone modified tris (acroxyethyl) isocyanurate (made by Toa GoseiCo., Ltd.; trade name: Acronix M315) as a photosensitive monomer, 2parts by weight of a photoinitiator (made by Ciba Geigy trade name:Irgaquar 907), 0.2 part by weight of a photosensitizer (made by NipponKayaku Co., Ltd.; trade name: DETX-S) and 30.0 parts by weight of epoxyresin particles (made by Sanyo Kasei Co., Ltd.; trade name: PolymerpoleS-031. The particle size distribution of these particles is shown inFIG. 25. An average particle size of these particles is 0.51 μm as amedian size and has a standard deviation of 0.193. These particles aredistributed within a range of 0.09-1.32 μm and a particle size in a peakof the particle size distribution is 0.58 μm and the peak is one as seenfrom FIG. 25. Moreover, the measurement of the particle sizedistribution is carried to by using Shimazu laser diffraction typeparticle size distribution measuring device SALD-2000 made by ShimazuSeisakusho.), adding 30.0 parts by weight of NMP (normal methylpyrolidone), adjusting a viscosity to 7 Pa·s in a homodisper agitatingmachine and kneading through three rolls.

(2) The adhesive solution for electroless plating obtained in the step(1) is applied to both surfaces of a core substrate by means of a rollcoater according to the steps (1), (2) of Example 1, left to stand athorizontal state for 20 minutes and dried at 60° C. for 30 minutes toform an adhesive layer 2 having a thickness of 60 μm.

(3) A polyethylene terephthalate film (light permeation film) isattached onto the adhesive layer 2 formed on each surface of thesubstrate in the step (2) through a tackifier. Then, sodalime glasssubstrate of 5 mm in thickness depicted with the same circle pattern(mask pattern) as the viahole through a light screen ink of 5 μm inthickness is closely placed onto the adhesive layer 2 so as to face thecircle pattern side thereto and exposed to an ultraviolet ray.

(4) The exposed substrate is developed by spraying DMTG (triethyleneglycol dimethyl ether) solution to from an opening of 100 μm as aviahole in the adhesive layer 2. Further, the substrate is exposed to asuper-high pressure mercury lamp at 3000 mJ/cm² and heated at 100° C.for 1 hour and at 150° C. for 5 hours to form an adhesive layer 2 of 45μm in thickness provided with the opening 6 (opening for the formationof viahole) having excellent dimensional accuracy corresponding to thephotomask. Moreover, the roughened layer 11 is partly exposed in theopening 6 as a viahole (see FIG. 7).

(5) The substrate provided with the opening 6 for the formation ofviahole is immersed in chromic acid for 2 minutes to dissolve and removethe epoxy resin particles existing in the surface area of the adhesivelayer 2, whereby the surface of the adhesive layer 2 is roughened andthen immersed in a neutral solution (made by Shipley) and washed withwater (see FIG. 8).

(6) On the other hand, a mixed solution A is prepared by mixing 46.7parts by weight of a photosensitized oligomer obtained by acrylating 50%of epoxy group in cresol novolac type epoxy resin (made by Nippon KayakuCo., Ltd.; trade name: ECON-103S) dissolved in DMDG, 15.0 parts byweight of 80 parts by weight of bisphenol A-type epoxy resin (made byYuka Shell Co., Ltd.; trade name: Epikote 1001) dissolved in methylethyl ketone), 1.6 parts by weight of imidazole curing agent (made byShikoku Kasei Co., Ltd.; trade name: 2E4MZ-CN), 3 parts by weight of apolyvalent acrylate (made by Nippon Kayaku Co., Ltd.; trade name: R-604)as a photosensitive monomer and 1.5 parts by weight of polyvalent acrylmonomer (made by Kyoei Kagaku Co., Ltd.; trade name: DPE-6A), adding 0.5part by weight of apolymer of acrylic ester (made by Kyoei Kagaku Co.,Ltd.; trade name: Polyflow 75) to total weight of the resulting mixtureand agitating them.

Further, a mixed solution B is prepared by dissolving 2 parts by weightof benzophenone (made by Kanto Kagaku Co., Ltd.) as a photoinitiator and0.2 part by weight of Michler's ketone (made by Kanto Kagaku Co., Ltd.)As a photosensitizer in 3 parts by weight of DMDG warmed at 40° C.

Then, the mixed solution A is mixed with the mixed solution B to form aliquid resist.

(7) The liquid resist is applied onto the substrate treated in the step(5) by means of a roll coater and dried at 60° C. for 30 minutes to forma resist layer having a thickness of 30 μm. Then, a mask film depictedwith a conductor circuit pattern of L/S (ratio of line to space)=50/50is closed, exposed to a super-high pressure mercury lamp at 1000 mJ/cm²and developed by spraying DMDG to form a plating resist removing theconductor circuit pattern portion in the substrate, which is furtherexposed to a super-high pressure mercury lamp at 6000 mJ/cm² and heatedat 100° C. for 1 hour and at 150° C. for 3 hours to form a permanentresist 3 on the adhesive layer 2 (interlaminar insulating resin layer)(see FIG. 21).

(8) The substrate provided with the permanent resist 3 is immersed in anaqueous solution of 100 g/l of sulfuric acid to activate a catalystnucleus, which is subjected to a primary plating in an electrolesscopper-nickel alloy plating bath having the following composition toform a thin plated film of copper-nickel-phosphorus alloy having athickness of about 1.7 μm on the portion not forming the resist. In thiscase, the temperature of the plating bath is 60° C. and the plating timeis 1 hour.

Metal salts CuSO₄ 5H2O : 6.0 mM (1.5 g/l) NiSO₄ 6H₂O : 95.1 mM (25 g/l)complexing agent Na₃C₆H₅O₇ : 0.23 M (60 g/l) Reducing agent NaPH₂O₂ H₂O: 0.19 M (20 g/l) pH adjusting agent NaOH : 0.75 M (pH = 9.5) Stabilizerlead nitrate : 0.2 M (80 ppm) Surfactant : 0.05 g/l

Moreover, the precipitation rate is 1.7 μm/h.

(9) The substrate subjected to the primary plating is taken out from theplating bath, washed with water to remove the plating solution adheredto the surface and further treated with an acidic solution to removeoxide film on the surface layer of copper-nickel-phosphorus thin platedfilm. Thereafter, the copper-nickel-phosphorus thin plated film issubjected to a secondary plating in an electroless copper plating bathhaving the following composition without Pd substitution to formouterlayer conductor pattern required as a conductor in additive processand viahole (BVH) (see FIG. 22). In this case, the temperature of theplating bath is 50-70° C. and the plating time is 90-360 minutes.

Metal salt CuSO4 5H2O : 8.6 mM Complexing agent TEA : 0.15 M Reducingagent HCHO : 0.02 M Others stabilizer : small amount (bipyridyl,potassium ferrocyanide and the like) Precipitation rate : 6 μm/h

(10) After the conductor layer is formed by additive process, theone-side surface of the substrate is polished by belt sander polishingwith a #600 belt polishing paper so as to align the upper surface of thepermanent resist, the upper surface of the conductor circuit and theupper land surface of the viahole to each other. Subsequently, buffingis carried out for removing the scratch produced by the belt sander(only the buffing may be sufficient). The other side surface issubjected to the same polishing as mentioned above to obtain a printedwiring substrate, both surfaces of which being smooth.

(11) The surface-smoothened printed wiring substrate is immersed in anelectroless plating solution of pH=9 containing 8 g/l of copper sulfate,0.6 g/l of nickel sulfate, 15 g/l of citric acid, 29 g/l of sodiumhypophosphorite, 31 g/l of boric acid and 0.1 g/l of surfactant to forma roughened layer 11 of copper-nickel-phosphorus alloy having athickness of 3 μm on the surface of the conductor exposed from thesurface of the substrate (see FIG. 23).

Thereafter, a conductor layer is further formed through additive processby repeating the above steps to form another wiring layer. In this way,there is provided a multilayer printed circuit board having 6 wiringlayers.

(12) Further, a solder resist layer 14 and a solder bump 17 are formedaccording to the steps (16)-(20) of Example 1 to produce a printedcircuit board having solder bumps 17 (see FIG. 24).

COMPARATIVE EXAMPLE 1

Semi-Additive Process (3.9 μm/0.5 μm)

The printed circuit board having solder bumps is produced in the samemanner as in Example 1 except that the following adhesive solution forelectroless plating is used.

That is, the photosensitive adhesive solution for electroless plating(interlaminar resin insulating agent) is prepared by mixing 34 parts byweight of 25% acrylated product of cresol novolac type epoxy resin (madeby Nippon Kayaku Co., Ltd.; molecular weight: 2500) dissolved in DMDG(diethylene glycol dimethyl ether), 12 parts by weight of polyethersulphone (PES), 2 parts by weight of imidazole curing agent (made byShikoku Kasei Co., Ltd.; trade name: 2E4MZ-CN), 4 parts by weight ofcaprolactone modified tris(acroxyethyl) isocyanurate (made by Toa GoseiCo., Ltd.; trade name: Aronix M315) as a photosensitive monomer, 2 partsby weight of a photoinitiator (made by Ciba Geigy trade name: Irgaquar907), 0.2 part by weight of a photosensitizer (made by Nippon KayakuCo., Ltd.; trade name: DETX-S), 10 parts by weight of epoxy resinparticles having an average particle size of 3.9 μm and 25 parts byweight of the epoxy resin particles having an average particle size of0.5 μm (made by Toray Co., Ltd.; trade name: Toreparle), adding 30.0parts by weight of NMP (normal methyl pyrolidone), adjusting a viscosityto 7 Pa·s in a homodisper agitating machine and kneading through threerolls.

COMPARATIVE EXAMPLE 2 Semi-Additive Process (1.6 μm groundpowder+epoxy/PES matrix)

(1) Epoxy resin particles are prepared according to a method describedin JP-A-61-276875 (U.S. Pat. No.4,752,499 and U.S. Pat. No.5,921,472).

That is, epoxy resin (made by Mitsui Petrochemical Industries, Ltd.;trade name: TA-1800) is cured by drying in a hot air dryer at 180° C.for 4 hours and the cured epoxy resin is roughly ground and sieved byusing a supersonic jet grinding machine (made by Nippon Pneumatic KogyoCo., Ltd.; trade name: Aqucut B-18 model) while freezing with a liquidnitrogen, whereby there are prepared epoxy resin particles having anaverage particle size of 1.6 μm.

(2) The production of the printed circuit board is carried out in thesame manner as in Example 1 except that the following adhesive solutionfor electroless plating is used.

That is, the photosensitive adhesive solution for electroless plating(interlaminar resin insulating agent) is prepared by mixing 34 parts byweight of 25% acrylated product of cresol novolac type epoxy resin (madeby Nippon Kayaku Co., Ltd.; molecular weight:2500) dissolved in DMDG(diethylene glycol dimethyl ether), 12 parts by weight of polyethersulphone (PES), 2 parts by weight of imidazole curing agent (made byShikoku Kasei Co., Ltd.; trade name: 2E4MZ-CN), 4 parts by weight ofcaprolactone modified tris (acroxyethyle) isocyanurate (made by ToaGosei Co., Ltd.; trade name: Aronix M315) as a photosensitive monomer, 2parts by weight of a photoinitiator (made by Ciba Geigy trade name:Irgaquar 907), 0.2 part by weight of a photosensitizer (made by NipponKayaku Co., Ltd.; trade name: DETX-S) and 35 parts by weight of theepoxy resin particles of the above step (1) having an average particlesize of 1.6 μm, adding 30.0 parts by weight of NMP (normal methylpyrolidone), adjusting a viscosity to 7 Pa·s in a homodisper agitatingmachine and then kneading through three rolls.

COMPARATIVE EXAMPLE 3 Semi-Additive Process 1.6 μm particles+epoxy/PESmatrix

The printed circuit board having solder bumps is produced in the samemanner as in Example 1 except that the following adhesive solution forelectroless plating is used.

That is, the photosensitive adhesive solution for electroless plating(interlaminar resin insulating agent) is prepared by mixing 34 parts byweight of 25% acrylated product of cresol novolac type epoxy resin (madeby Nippon Kayaku Co., Ltd.; molecular weight:2500) dissolved in DMDG(diethylene glycol dimethyl ether), 12 parts by weight of polyethersulphone (PES), 2 parts by weight of imidazole curing agent (made byShikoku Kasei Co., Ltd.; trade name: 2E4MZ-CN), 4 parts by weight ofcaprolactone modified tris (acroxyethyle) isocyanurate (made by ToaGosei Co., Ltd.; trade name: Aronix M315) as a photosensitive monomer, 2parts by weight of a photoinitiator (made by Ciba Geigy trade name:Irgaquar 907), 0.2 part by weight of a photosensitizer (made by NipponKayaku Co., Ltd.; trade name: DETX-S) and 35 parts by weight of theepoxy resin particles (made by Toray Co., Ltd.; trade name: Toreparle)having an average particle size of 1.6 μm, adding 30.0 parts by weightof NMP (normal methyl pyrolidone), adjusting a viscosity to 7 Pa·s in ahomodisper agitating machine and then kneading through three rolls.

COMPARATIVE EXAMPLE 4 Full-Additive Process (3.9 μm/0.5 μm)

The printed circuit board having solder bumps is produced in the samemanner as in Example 3 except that the following adhesive solution forelectroless plating is used.

That is, the photosensitive adhesive solution for electroless plating(interlaminar resin insulating agent) is prepared by mixing 34 parts byweight of 25% acrylated product of cresol novolac type epoxy resin (madeby Nippon Kayaku Co., Ltd.; molecular weight: 2500) dissolved in DMDG(diethylene glycol dimethyl ether), 12 parts by weight of polyethersulphone (PES), 2 parts by weight of imidazole curing agent (made byShikoku Kasei Co., Ltd.; trade name: 2E4MZ-CN), 4 parts by weight ofcaprolactone modified tris (acroxyethyle) isocyanurate (made by ToaGosei Co., Ltd.; trade name: Aronix M315) as a photosensitive monomer, 2parts by weight of a photoinitiator (made by Ciba Geigy trade name:Irgaquar 907), 0.2 part by weight of a photosensitizer (made by NipponKayaku Co., Ltd.; trade name: DETX-S), 10 parts by weight of the epoxyresin particles (made by Toray Co., Ltd.; trade name: Toreparle) havingan average particle size of 3.9 μm and 25 parts by weight of the epoxyresin particles having an average particle size of 0.5 μm, adding 30.0parts by weight of NMP (normal methyl pyrolidone), adjusting a viscosityto 7 Pa·s in a homodisper agitating machine and then kneading throughthree rolls.

COMPARATIVE EXAMPLE 5 Full-Additive Process 1.6 μm groundpowder+epoxy/PES matrix

(1) Epoxy resin particles are prepared according to a method describedin JP-A-61-276875.

That is, epoxy resin (made by Mitsui Petrochemical Industries, Ltd.;trade name: TA-1800) is cured by drying in a hot air dryer at 180° C.for 4 hours and the cured epoxy resin is roughly ground and sieved byusing a supersonic jet grinding machine (made by Nippon Pneumatic KogyoCo., Ltd.; trade name: Aqucut B-18 model) while freezing with a liquidnitrogen, whereby there are prepared epoxy resin particles having anaverage particle size of 1.6 μm.

(2) The production of the printed circuit board is carried out in thesame manner as in Example 3 except that the following adhesive solutionfor electroless plating is used.

That is, the photosensitive adhesive solution for electroless plating(interlaminar resin insulating agent) is prepared by mixing 34 parts byweight of 25% acrylated product of cresol novolac type epoxy resin (madeby Nippon Kayaku Co., Ltd.; molecular weight: 2500) dissolved in DMDG(diethylene glycol dimethyl ether), 12 parts by weight of polyethersulphone (PES), 2 parts by weight of imidazole curing agent (made byShikoku Kasei Co., Ltd.; trade name: 2E4MZ-CN), 4 parts by weight ofcaprolactone modified tris (acroxyethyle) isocyanurate (made by ToaGosei Co., Ltd.; trade name: Aronix M315) as a photosensitive monomer, 2parts by weight of a photoinitiator (made by Ciba Geigy trade name:Irgaquar 907), 0.2 part by weight of a photosensitizer (made by NipponKayaku Co., Ltd.; trade name: DETX-S) and 35 parts by weight of theepoxy resin particles of the above step (1) having an average particlesize of 1.6 μm, adding 30.0 parts by weight of NMP (normal methylpyrolidone), adjusting a viscosity to 7 Pa·s in a homodisper agitatingmachine and then kneading through three rolls.

COMPARATIVE EXAMPLE 6 Full-Additive Process 1.6 μm particles+epoxy/PESmatrix

The printed circuit board having solder bumps is produced in the samemanner as in Example 3 except that the following adhesive solution forelectroless plating is used.

That is, the photosensitive adhesive solution for electroless plating(interlaminar resin insulating agent) is prepared by mixing 34 parts byweight of 25% acrylated product of cresol novolac type epoxy resin (madeby Nippon Kayaku Co., Ltd.; molecular weight:2500) dissolved in DMDG(diethylene glycol dimethyl ether), 12 parts by weight of polyethersulphone (PES), 2 parts by weight of imidazole curing agent (made byShikoku Kasei Co., Ltd.; trade name: 2E4MZ-CN), 4 parts by weight ofcaprolactone modified tris (acroxyethyle) isocyanurate (made by ToaGosei Co., Ltd.; trade name: Aronix M315) as a photosensitive monomer, 2parts by weight of a photoinitiator (made by Ciba Geigy trade name:Irgaquar 907), 0.2 part by weight of a photosensitizer (made by NipponKayaku Co., Ltd.; trade name: DETX-S) and 35 parts by weight of theepoxy resin particles (made by Toray Co., Ltd.; trade name: Toreparle)having an average particle size of 1.6 μm, adding 30.0 parts by weightof NMP (normal methyl pyrolidone), adjusting a viscosity to 7 Pa·s in ahomodisper agitating machine and then kneading through three rolls.

COMPARATIVE EXAMPLE 7 Semi-Additive Process 5.5 μm/0.5 μm (JP-A-7-34048,U.S. Pat. No. 5,519,177)

The printed circuit board having solder bumps is produced in the samemanner as in Example 1 except that the following adhesive solution forelectroless plating is used.

That is, the photosensitive adhesive solution for electroless plating(interlaminar resin insulating agent) is prepared by mixing 34 parts byweight of 25% acrylated product of cresol novolac type epoxy resin (madeby Nippon Kayaku Co., Ltd.; molecular weight:2500) dissolved in DMDG(diethylene glycol dimethyl ether), 12 parts by weight of polyethersulphone (PES), 2 parts by weight of imidazole curing agent (made byShikoku Kasei Co., Ltd.; trade name: 2E4MZ-CN), 5 parts by weight oftrimethyl triacrylate (TMPTA) as a photosensitive monomer, 2 parts byweight of a photoinitiator (made by Ciba Geigy trade name: Irgaquar907), 10 parts by weight of the epoxy resin particles (made by TorayCo., Ltd.; trade name: Toreparle) having an average particle size of 5.5μm and 5 parts by weight of the epoxy resin particles having an averageparticle size of 0.5 μm, adding 30.0 parts by weight of NMP (normalmethyl pyrolidone), adjusting a viscosity to 7 Pa·s in a homodisperagitating machine and then kneading through three rolls.

COMPARATIVE EXAMPLE 8 Full-Additive Process 5.5 μm/0.5 μm (JP-A-7-34048,U.S. Pat. No. 5,519,177)

The printed circuit board having solder bumps is produced in the samemanner as in Example 3 except that the following adhesive solution forelectroless plating is used.

That is, the photosensitive adhesive solution for electroless plating(interlaminar resin insulating agent) is prepared by mixing 34 parts byweight of 25% acrylated product of cresol novolac type epoxy resin (madeby Nippon Kayaku Co., Ltd.; molecular weight: 2500) dissolved in DMDG(diethylene glycol dimethyl ether), 12 parts by weight of polyethersulphone (PES), 2 parts by weight of imidazole curing agent (made byShikoku Kasei Co., Ltd.; trade name: 2E4MZ-CN), 5 parts by weight oftrimethyl triacrylate (TMPTA) as a photosensitive monomer, 2 parts byweight of a photoinitiator (made by Ciba Geigy trade name: Irgaquar907), 10 parts by weight of the epoxy resin particles (made by TorayCo., Ltd.; trade name: Toreparle) having an average particle size of 5.5μm and 5 parts by weight of the epoxy resin particles having an averageparticle size of 0.5 μm, adding 30.0 parts by weight of NMP (normalmethyl pyrolidone), adjusting a viscosity to 7 Pa s in a homodisperagitating machine and then kneading through three rolls.

EXAMPLE 4

Example using material composition for the preparation of the adhesiveeach preserved in separated manner.

The printed circuit board is produced in the same manner as in Example 1except that the adhesive for electroless plating is prepared by thefollowing groups 1-3 of material compositions.

A. Material compositions for the preparation of adhesive for electrolessplating(adhesive for upper layer).

<Group 1>

35 parts by weight of 25% acrylated product of cresol novolac type epoxyresin (2500 in molecular weight, made by Nippon Kayaku Co., Ltd.) as a80% by weight solution in DMDG(diethylene glycol dimethyl ether), 4parts by weight of a photosensitive monomer(made by Toa Gosei Co.,Ltd.,trade name: Aronix M315), 0.5 parts by weight of antiforming agent(made by SANNOPCO, tradename: S-65), and 3.6 parts by weight of NMP aremixed together by agitation to obtain group 1 composition.

<Group 2>

8 parts by weight of polyether sulfone (PES), 7.245 parts by weight ofepoxy resin having an average particle size of 0.5 μm (POLYMERPOLE bySanyo Kasei Co., Ltd.) are mixed together and then 20 parts by weight ofNMP were added to the mixture. They are mixed together by agitation toobtain group 2 composition.

<Group 3>

2 parts by weight of imidazole curing agent (2E4MZ-CN by Shikoku KaseiCo., Ltd.), 2 parts by weight of photoinitiator (IRGACURE I-907 by CibaGeigy), 0.2 part by weight of photosensitizer (DETX-S by Nippon KayakuCo., Ltd.) and 1.5 parts by weight of NMP are mixed together byagitation to obtain group 3 composition.

These compositions of groups 1-3 are preserved in a separated manner toone another at the temperature of 25° C. a month.

B. Material Compositions for the preparation of interlaminar insulatingresin agent(adhesive for lower layer).

<Group 1>

35 parts by weight of 25% acrylated product of cresol novolac type epoxyresin (2500 in molucular weight, by Nippon Kayaku Co., Ltd.) as a 80% byweight solution in DMDG (diethylene glycol dimethyl ether), 4 parts byweight of a photosensitive monomer(made by Toa Gosei Co., Ltd.,tradename: Aronix M315), 0.5 parts by weight of antiforming agent(made bySANNOPCO, tradename: S-65), and 3.6 parts by weight of NMP, are mixedtogether by agitation to obatin group 1 composition.

<Group 2>

8 parts by weight of polyether sulfone (PES), 14.49 parts by weight ofepoxy resin having the average particle size of 0.5 μm (POLYMERPOLE bySanyo Kasei Co., Ltd.) are mixed together and then 30 parts by weight ofNMP are added to the mixture. They are mixed together by agitation toobtain group 2 composition.

<Group 3>

2 parts by weight of imidazole curing agent (2E4MZ-CN by Shikoku KaseiCo., Ltd.), 2 parts by weight of photoinitiator (IRGACURE I-907 by CibaGeigy), 0.2 part by weight of photosensitizer(DETX-S by Nippon KayakuCo., Ltd.) and 1.5 parts by weight of NMP are mixed together byagitation to obtain group 3 composition.

These compositions of groups 1-3 are preserved in a separated manner toone another at the temperature of 25° C. for a month.

C. Material Compositions for the preparation of resin filler.

<Group 1>

100 parts by weight of a bisphenol F type epoxy monomer (manufactured byYuka Shell Co., Ltd., 310 in molecular weight, tradename: YL983U), 170parts by weight of spherical SiO₂ particles (manufactured by AdmatechCo., Ltd., tradename: CRS 1101-CE, where the maximum particle size isset to below the thickness (15 μm) of an internal layer copper patternmentioned below) coated with a silane coupling agent on their surfacesand having an average particle size of 1.6 μm, and 1.5 parts by weightof a leveling agent (manufactured by Sannopko, tradename: Pernol S4) aremixed together by agitation, and adjusted in viscosity to the range from45,000 to 49,000 cps at 23±1° C. to obtain group 1 composition.

<Group 2>

Imidazole curing agent (manufactured by Shikoku Kasei Co., Ltd.,2E4MZ-CN) of 6.5 parts by weight.

The compositions of groups 1 and 2 are preserved in a separated mannerto each other at the temperature of 25° C. for a month.

D. Material compositions for the preparation of the liquid solderresist.

<Group 1>

100 parts by weight of a photosensitized oligomer (4,000 in molecularweight) obtained by acrylating 50% of epoxy groups of a cresol novolactype epoxy resin (manufactured by Nippon Kayaku Co., Ltd.), 32 parts byweight of a bisphenol A type epoxy resin (manufactured by Yuka ShellCo., Ltd., trade name: Epikote 1001) as a 80% by weight solution inmethyl ethyl ketone, 6.4 parts by weight of a polyvalent acrylic monomer(manufactured by Nippon Kayaku Co., Ltd., R604) as a photosensitivemonomer, and 3.2 parts by weight of a polyvalent acrylic monomer(manufactured by Kyoeisha Chemical Co., Ltd., DPE6A), are mixed, andthen 0.5 part by weight of a leveling agent (manufactured by KyoeishaChemical Co., Ltd., Polyflow No. 75) is added to the mixture and mixedtogether by agitation to obtain group 1 composition.

<Group 2>

3.4 parts by weight of imidazole curing agent (manufactured by ShikokuKasei Co., Ltd., 2E4MZ-CN), 2 parts by weight of photoinitiator(IRGACURE I-907 by Ciba Geigy), 0.2 parts by weight of a photosensitizer(DETX-S by Nippon Kayaku Co., Ltd. ), and 1.5 part by weight of NMP aremixed together by agitating to obtain group 2 composition.

The compositions of groups 1 and 2 are preserved in a separated mannerto each other at the temperature of 25° C. for a month.

E. Manufacturing of the Printed Circuit Board.

(1) The steps (1) and (2) of the Example 1 are caried out.

(2) The material compositons B for the preparation of the interlaminarinsulating resin agent are mixed together by agitation, and adjusted inviscosity to 1.5 Pa·s to obtain an interlaminar insulating resin agent(for lower layer).

The material compositions A for the preparation of adhesive forelectroless plating are mixed together by agitating, and adjusted inviscosity to 7 Pa·s to obtain an adhesive solution for the electrolessplating (for upper layer).

(3) The interlaminar insulating resin agent (for the lower layer) havingthe viscosity of 1.5 Pa·s prepared at the above step (2) is applied toboth surfaces of the substrate within 24 hours after preparing thecompostions B, by means of a roll coater and left to stand at horizontalstate for 20 minutes and dried (pre-bake) at 60° C. for 30 minutes, andthen the adhesive solution (for the upper layer) having the viscosity of7 Pa·s prepared at the above step (2) is applied to the former layerswithin 24 hours after preparing the compostions A, and left to stand athorizontal state for 20 minutes and dried (pre-bake) at 60° C. for 30minutes to form an adhesive layer (two-layer structure) of 35 μm (seeFIG. 6(b)).

The two-layer structure will be omitted in the drawings as from FIG. 7.

(4) A photomask film depicted with a full circle (black circle) of 85 μmin diameter is attached to both surfaces of the adhesive layers 12formed on both surfaces of the substrate in the above step (3) andexposed to a light irradiation at 500 mJ/cm² by an ultra-high pressuremercury lamp. The exposed substrate is developed by spraying a DMDG(diethylene glycol dimethyl ether) solution, and further exposed to alight irradiation at 3,000 mJ/cm² by an ultra-high pressure mercury lampand heated at 100° C. for 1 hour and subsequently at 120° C. for 1 hourand then heated at 150° C. for 3 hours (post-bake) to form aninterlaminar insulating material layer (two-layer structure) 2 of 35 μmin thickness provided with openings (openings 6 for the formation ofviahole) having excellent dimensional precision corresponding to thephotomask film (see FIG. 7). Incidentally, the tin plated layer ispartly exposed in the opening for the viahole.

(5) The substrate provided with the openings 6 for the formation ofviahole is immersed in chromic acid for 19 minutes to dissolve andremove the epoxy resin particles on the surface of the adhesive layer 2,whereby the surface of the adhesive layer 2 is roughened, and thenimmersed in a neutralizing solution (manufactured by Shipley) and washedwith water.

Further, catalyst nuclei are applied to the surfaces of the adhesivelayer 2 and the openings 6 for the formation of viahole by giving apalladium catalyst (manufactured by Atotech Co., Ltd.) to the substratehaving the roughened surface (roughened depth: 3 μm) of the adhesivelayer.

(6) The substrate is immersed in an electroless copper plating bathhaving the below composition to form an electroless copper plated film12 of 0.6 μm in thickness all over the roughened surface (see FIG. 9).

[Electroless plating solution] EDTA 150 g/l Copper sulfate 20 g/l HCHO30 ml/l NaOH 40 g/l α,α′-bipyridyl 80 mg/l PEG 0.1 g/l

(7) A commercially available photosensitive dry film is adhered to theelectroless copper plated film 12, and a mask is placed onto the dryfilm, exposed to a light at 100 mJ/cm² and developed with a 0.8% sodiumcarbonate solution to form a plating resist 15 having a thickness of 15μm (see FIG. 10).

(8) The substrate is then subjected to an electrolytic copper platingunder the below condition to form an electrolytic copper plated film 13having a thickness of 15 μm (see FIG. 11).

[Electrolytic plating solution] sulfuric acid 180 g/l copper sulfate  80g/l additive (made by Atoteck Japan,  1 ml/1 trade name: Capalacid GL)[Electrolytic plating condition] current density  1.0 A/dm² time  30minutes temperature Room temperature

(9) After the plating resist is peeled off by spraying a 5% KOHsolution, the electroless plated film 12 located beneath the platingresist 13 is dissolved and removed by etching with a mixed solution ofsulfuric acid and hydrogen peroxide to form conductor circuits(inclusive of viaholes) each consisting of the electroless copper platedfilm 12 and the electrolytic copper plated film 13 and having athickness of 18 μm (see FIG. 12).

(10) Pd remained in the roughened surface of the adhesive layer 12 wasremoved by immersing in chromic acid (800 g/l) for 1 to 10 minutes.

The multilayer printed wiring board prepared by the above mentionedmanner ensures through-holes each provided with a perfectly circularland, and it can provide a land pitch of about 600 μm and therebythrough-holes can be formed in a high density so as to densifythrough-holes easily. In addition, since the number of through-holes inthe substrate can be increased, an electric connection with respect toconductor circuits in the multilayer core substrate can sufficiently beensured through the through-holes.

(10) The substrate provided with the conductor circuit is immersed in anelectroless plating solution of pH=9 containing 8 g/l of copper sulfate,0.6 g/l of nickel sulfate, 15 g/l of citric acid, 29 g/l of sodiumhypophosphite, 31 g/l of boric acid and 0.1 g/l of surfactant to form aroughened layer 11 of copper-nickel-phohsphorus having a thickness of 3μm on the surface of the conductor circuit (see FIG. 13). In this case,the roughened layer 11 has a composition ratio of Cu: 98 mol %, Ni: 1.5%and P: 0.5 mol % as analyzed by EPMA (fluorescent X-ray analyzingdevice).

Further, the substrate is subject to Cu—Sn substitution plating underthe condition of the plating bath containing 0.1 mol/l of tinborofluoride and 1.0 mol/l of thiourea, the temperature being 50° C. andpH being 1.2 to form a tin substitution plated layer of 0.3 μm on thesurface of the roughened layer 11 (see FIG. 13 provided that tinsubstituted layer is not shown).

(11) Further, conductor circuits are formed by repeating the steps(2)-(10) to form a multilayer printed circuit board. In this case, thetin substitution plated layer is not formed on the surface of theroughened layer (see FIGS. 14-19).

(12) Furthermore, a solder resist layer and a solder bump are formedaccording to the steps (16)-(20) of Example 1 to produce a printedcircuit board having solder bumps (see FIG. 20).

The roughened surfaces of the conductor circuit and interlaminarinsulating resin layer formed according to Example 3 are subject tomeasurement of the count value of irregularity level by means of Atomicforce microscope (AFM by Olympus Optical Co., Ltd, tradename: NV3000).In these measurements, the count value is obtained within a scanningrange of 50 μm, however, Tables 1 and 2 show fifty times multiplicationof the actual count value, i.e. the count value of irregularity level atthe surface length of 2.5 mm is shown in Tables 1 and 2.

As shown in FIGS. 1 and 2, in the printed circuit board using theadhesive for electroless plating according to the present invention, thecount value of irregularity level at the surface length of 2.5 mm withrespect to the roughened surface of the adhesive layer is comparativelysmall, i.e. 50-1300 for the peak count 0.01≦Pc≦0.1 μm, and 200-500 forthe peak count 0.1≦Pc≦1.0 μm, respectively, and residues in the platingresist, electroless plating and Pd catalyst are not found.

Further, the count value with respect to the roughened surface formed onthe surface of the conductor circuit is also comparatively small, i.e.350-650 for the peak count 0.01≦Pc≦0.1 μm, and 600-1150 for the peakcount 0.1≦Pc≦1.0 μm, at the surface length of 2.5 mm, respectively,thereby causing less delay in signal propagation in the conductorcircuit.

TABLE 1 Conductor circuit Cut Off 0 ≦ Pc ≦ 0.01 (μm) 0.01 ≦ Pc ≦ 0.1(μm) 0.1 ≦ Pc ≦ 1.0 (μm) 1 0 350 600 1/5 0 500 700 1/20 150  650 1150 

TABLE 2 Interlaminar Insulating resin layer Cut Off 0 ≦ Pc ≦ 0.01 (μm)0.01 ≦ Pc ≦ 0.1 (μm) 0.1 ≦ Pc ≦ 1.0 (μm) 1 0  150 350 1/5 0  50 500 1/20450  1300 200

COMPARATIVE EXAMPLE 9

The printed circuit board having solder bumps is produced in the samemanner as in Example 1 except that the thickness of the interlaminarinsulating resin layer is formed to be 35 μm, however, breakage of theinterlaminar insulation was found in the roughening treatment.

The tests and evaluations as mentioned below are carried out withrespect to the printed circuit boards of the examples and comparativeexamples.

{circle around (1+L )}. The peel strength is measured according toJIS-C-6481 in the circuit boards of Examples 1-3 and ComparativeExamples 1-8.

{circle around (2+L )}. In the circuit boards of Examples 1-3 andComparative Examples 1-8, the depth of depression of the roughenedsurface is measured by cross-cutting the circuit board and observing thecut section by means of a metal microscope.

{circle around (3+L )}. The surface resistivity is measured with respectto the circuit boards of Examples 1 and 2 and Comparative Examples 1-3and 7.

{circle around (4+L )}. In the circuit boards of Example 3 andComparative Examples 4-6 and 8, the surface resistivity is measuredafter the circuit board is left to stand under conditions of humidity of85%, temperature of 130° C. and voltage of 3.3 V for 48 hours.

{circle around (5+L )}. The presence or absence of cracks is measured byheat cycle test of −55° C.˜125° C. at 500 times with respect to thecircuit boards of Examples 1-3 and Comparative Examples 1-8.

{circle around (6+L )}. The L/S forming limit is measured with respectto the circuit boards of Examples 1-3 and Comparative Examples 1-8.

{circle around (7+L )}. The heating test is carried out with respect tothe circuit boards of Examples 1-3 and Comparative Examples 1-8.

The test is carried out under the conditions of 128° C. and 48 hours.According to this heating test, if the resin remains in the openingportion for the formation of viahole, the peeling of viahole is caused.The presence or absence of such a peeling is measured by the conductionresistance of the viahole, whereby the peeling of viahole is confirmedto be caused when the conduction resistance is raised.

{circle around (8+L )}. In the circuit boards of Examples 1-3 andComparative Examples 1-8, the ratio of generating interlaminarinsulation breakage is measured by preparing 100 circuit boards.

The test results are shown in Table 3.

TABLE 3 Particle Surface resistivity size of heat- Depression afterbeing left to Ratio of resistant depth of Surface stand under high-insulation resin Peel roughened resist- temperature and high- L/SPeeling breakage particle strength surface ivity humidity conditionslimit of generated (μm) (kg/cm) (μm) (Ω) (Ω) Cracks (μm) viahole (%)Example 1 0.51 1.0 3 2 × 10¹⁴ not measured absence 20/20 absence 0 20.92 1.0 3 1 × 10¹⁴ not measured absence 20/20 absence 0 3 0.51 1.0 3not 3 × 10¹² (2) 20/20 absence 0 measured Compar- 1 mixture 1.9 10  4 ×10⁸ not measured absence 40/40 absence 10  ative 3.9/0.5 Example 2ground 1.4 4  8 × 10¹³ not measured presence 20/20 presence 0 particle1.6 (1) 3 spherical 1.0 4  1 × 10¹⁴ not measured absence 20/20 presence0 particle 1.6 4 mixture 2.0 10  not 5 × 10¹⁰ presence 40/40 absence 10 3.9/0.5 measured (2) 5 ground 1.4 4 not 7 × 10¹¹ presence 20/20 presence0 particle 1.6 measured (1) (2) 6 spherical 1.0 4 not 2 × 10⁸  presence20/20 presence 0 particle 1.6 measured (2) 7 mixture 2.6 11  2 × 10⁸ notmeasured absence 45/45 absence 15  5.5/0.5 8 mixture 2.7 11  not 2 ×10¹⁰ presence 45/45 absence 15  5.5/0.5 measured (2) (1) crack startingfrom anchor of conductor circuit (2) crack starting from boundarybetween plating resist and conductor circuit

{circle around (1+L )} As seen from the results of the above table, whenusing the adhesive for electroless plating according to the invention,the depth of depression in the roughened surface is shallower (3 μm) ascompared with the conventional one and hence the practical peel strengthof 1.0 kg/cm can be attained. In the printed circuit board according tothe invention, therefore, it is possible to make L/S of the patternsmaller.

{circle around (2+L )} The heat-resistant resin particles used in theadhesive for electroless plating and the printed circuit board accordingto the present invention are not more than 1.5 μm in the averageparticle size and less than 2 μm in the maximum particle size as seenfrom the particle size distribution, so that gaps between the layers arenot caused by the roughening treatment and there is no interlaminarinsulation breakage through conduction between the upper layer and thelower layer.

{circle around (3+L )} When the opening for the formation of viahole isformed in the interlaminar insulating resin layer of the substratehaving the roughened surface of the conductor circuit at the underlayerside, the resin remains in the roughened surface. In this connection,when Examples 1, 2 are compared with Comparative Examples 2 and 3, sincefine particles of not more than 1 μm are existent, it is possible toremove the resin residue in the roughening treatment, so that it isguessed that the peeling of viahole is not caused even in the heatingtest.

{circle around (4+L )} The surface resistivity in the circuit board ofExamples 1, 2 is higher than those of Comparative Examples 1, 7. It isconsidered that in the circuit board of Comparative Example 1, theelectroless plated film is retained because the depression of theroughened surface is too deep.

{circle around (5+L )} In the circuit board of Example 3, the surfaceresistivity does not lower even under high temperature and high humidityconditions. On the contrary, when the circuit boards of ComparativeExamples 4, 8 are exposed to high temperature and high humidityconditions, the surface resistivity lowers. This is presumed that in thecircuit boards of Comparative Examples 4, 8, the depression of theroughened surface is deeper than that in Example 3, so that a greateramount of Pd catalyst nucleus is attached and results in the lowering ofthe surface resistivity.

{circle around (5+L )} In the circuit boards of Examples 1, 2 andComparative Examples 1, 7, there is caused no cracks in the heat cycle.On the contrary, the circuit boards of Example 3 and ComparativeExamples 4, 5, 6, 8 cause the crack in the interlaminar insulating resinlayer (adhesive layer for electroless plating) starting from theboundary between the plating resist and the conductor circuit.

{circle around (6+L )} In the circuit boards of Comparative Examples 2,5, cracks starting from the anchor depression beneath the conductorcircuit is caused in the adhesive layer for electroless plating. This isconsidered due to the fact that since the ground powder is sharp in thecorner, the resulting anchor depression is also sharp and stressconcentration is caused therein in the heat cycle to cause cracks. Thatis, when the ground powder is used, the peel strength is improved, butthe cracks are caused in the heat cycle.

{circle around (7+L )} In the adhesive for electroless plating ofExample 1, gelation occurred after a month from mixing the compositions,and the adhesive has become too high in viscosity to be coated on thesubstrate, while in the adhesive for electroless plating of Example 3,lowering of the coating property was not found.

Moreover, the example of JP-A-61-276875 uses epoxy modified polyimideresin as a resin matrix, so that the toughness value is higher than thatof epoxy-PES resin and the peel strength of 1.6 kg/cm is obtained.

INDUSTRIAL APPLICABILITY

As mentioned above, in the adhesive for electroless plating according tothe present invention, the practical peel strength can be ensured, andthe surface resistivity is high and also the fine pattern of L/S=20/20μm can be formed, so that there can be provided the printed circuitboard having no interlaminar insulation breakage through the rougheningtreatment.

Further, in the adhesive for electroless plating according to thepresent invention, the adhesive resin remaining in the bottom of theopening for viahole can be removed in the roughening treatment, so thatthe printed circuit board using such an adhesive does not cause thepeeling of viahole in the heating test.

What is claimed is:
 1. An adhesive for electroless plating formed bydispersing cured heat-resistant resin particles soluble in acid oroxidizing agent into uncured heat-resistant resin matrix hardly solublein acid or oxidizing agent through curing treatment, characterized inthat the heat-resistant resin particles have an average particle size ofnot more than 1.5 μm.
 2. The adhesive for electroless plating accordingto claim 1, wherein the heat-resistant resin particles have an averageparticle size of 0.1-1.0 μm.
 3. An adhesive for electroless platingaccording to claim 1, wherein the heat-resistant resin particles arespherical particles.
 4. The adhesive for electroless plating accordingto claim 1, wherein the heat-resistant resin particles have a particlesize distribution such that the particles do not have a particle size ina peak of the distribution which is more than 1.5 μm.
 5. The adhesivefor electroless plating according to claim 1, wherein a particle sizedistribution of the heat resistant particles has one peak in theparticle size distribution.
 6. The adhesive for electroless platingaccording to claim 1, wherein the heat-resistant resin particles is5-50% by weight to a solid of the heat-resistant resin matrix.
 7. Theadhesive for electroless plating according to claim 1, wherein theheat-resistant resin matrix is a composite of the thermoseting resin andthermoplastic resin.
 8. The adhesive for electroless plating accordingto claim 7, wherein the thermoplatic resin is not more than 30% byweight of a solid content of the heat-resistant resin matrix.
 9. Aprinted circuit board comprising a substrate, a cured adhesive layer forelectroless plating having a roughened surface, and a conductor circuitformed on the roughened surface of the adhesive layer, said adhesivelayer being composed of an adhesive for electroless plating formed bydispersing cured heat-resistant resin particles soluble in acid oroxidizing agent into uncured heat-resistant resin matrix hardly solublein acid or oxidizing agent through curing treatment, said heat-resistantresin particles having an average particle size of not more than 1.5 μm.10. The printed circuit board according to claim 9, wherein theheat-resistant resin particles have an average particle size of 0.1-1.0μm.
 11. The printed circuit board according to claim 9, wherein theheat-resistant resin particles are spherical particles.
 12. The printedcircuit board according to claim 9, wherein the heat-resistant resinparticles have a particle size distribution such that the particles donot have a particle size in a peak of the distribution which is morethan 1.5 μm.
 13. The printed circuit board according to claim 9, whereina particle size distribution of the heat-resistant particles has onepeak in the particle size distribution.
 14. The printed circuit boardaccording to claim 9, wherein the roughened surface of the adhesivelayer has a depression depth R_(max)=1-5 μm.
 15. The printed circuitboard according to claim 9, wherein the depth of said roughened surfaceis 1-5 μm, a count value of the peak (Pc) of the roughness per a 2.5 mmlength of the surface, where 0.01≦Pc<0.1 μm, is 10-2500, and a countvalue of the peak (Pc) of the roughness per a 2.5 mm length of thesurface, where 0.1≦Pc<1.0 μm, is 100-1000.
 16. The printed circuit boardaccording to claim 9, wherein the heat-resistant resin particles is5-50% by weight of a solid of the heat-resistant resin matrix.
 17. Aprinted circuit board comprising a substrate, a conductor circuit formedon the substrate, an adhesive layer for electroless plating formed bydispersing cured heat-resistant resin particles soluble in acid oroxidizing agent into uncured heat-resistant resin matrix hardly solublein acid or oxidizing agent through curing treatment, a roughened surfaceformed on a surface of the adhesive layer by dissolving and removing thecured heat-resistant particles, and an upper conductor circuit is formedon the roughened surface, said adhesive layer for electroless platinghas more heat-resistant particles at the side of the substrate than thatat the opposite side thereof.
 18. The printed circuit board according toclaim 17, wherein the adhesive layer is formed in double-layer, and theheat-resistant particles in the adhesive layer at the side of thesubstrate is 20-50% by weight of a solid content of the heat-resistantresin matrix, and the heat-resistant particles in the adhesive layer atthe opposite side of the substrate is not less than 5% by weight butless than 20% by weight of a solid content of the heat-resistant resinmatrix.
 19. The printed circuit board according to claim 17, wherein theheat-resistant resin particles have an average particle size of 0.1-1.0μm.
 20. The printed circuit board according to claim 9, wherein theheat-resistant resin matrix is a composite of the thermoseting resin andthermoplastic resin.
 21. The printed circuit board according to claim 9,wherein the thermoplatic resin is not more than 30% by weight of a solidcontent of the heat-resistant resin matrix.
 22. The printed circuitboard according to claim 20, wherein the heat-resistant resin matrix isa composite of epoxy resin and a polyether sulphone, and the polyethersulphone in the composite is not more than 30% by weight of a solidcontent of the heat-resistant resin matrix.
 23. The printed circuitboard according to claim 9, wherein viaholes having diameter of lessthan 100 μm are formed in the adhesive layer.
 24. The printed circuitboard according to claim 9, wherein the adhesive layer has a thicknessof less than 50 μm.
 25. The printed circuit board according to claim 9,wherein the conductor circuit formed on the roughened surface of theadhesive layer is comprised of an electroless plated film and anelectrolytic plated film.
 26. The printed circuit board according toclaim 9, wherein the conductor circuit formed on the roughened surfaceof the adhesive layer has a roughened layer formed on at least a part ofthe conductor circuit.
 27. The printed circuit board according to claim9, wherein a conductor circuit is formed on a surface of the substrate,said conductor circuit having at least a part thereof a roughendsurface.
 28. A material composition for preparing an adhesive forelectroless plating, comprising: a resin composition of a first groupcomprising uncured thermosetting resin which becomes hardly soluble inan acid or oxidizing agent through curing treatment; a resin compositionof a second group comprising cured heat-resistant resin particlessoluble an acid or oxidizing agent and having an average particle sizeof not more than 1.5 μm, thermoplastic resin, and organic solvent; and acuring agent composition of a third group, wherein each group isprepared in advance for mixture, and preserved separately from oneanother.
 29. The material composition according to claim 28, wherein thea mixing ratio of the heat-resistant resin particles is 5-50% by weightof a solid of the heat-resistant resin matrix in the prepared adhesiveagent, as a weight ratio.
 30. The material composition, according toclaim 28, wherein a weight ratio between the thermosetting resin of thefirst group and the thermoplastic resin of the second group is¼˜{fraction (4/1)}.